Full frame camera recommendations - Canon 5DII, Nikon D700, Sony A900 and A850

Since I own Sony A900 I will try to compare it and Sony A850 to some other popular new cameras and tell you which one is better for what purpose.

Let's take a look at A900 by itself: 
    *  24.6 MP 35mm format full-frame CMOS sensor
    * Full frame image sensor shift stabilization
    * High Speed Dual Bionz processors
    * Eye-level glass Penta-prism OVF, 100% coverage, 0.74x magnification
    * 9 point AF with 10 assist points, center dual-cross AF w/2.8 sensor
    * 5 frames per second burst, newly developed mirror box
    * Intelligent Preview Function
    * Advanced Dynamic Range Optimizer (5 step selectable)
    * 40 segment honeycomb metering
    * 3.0" 921K pixel Photo Quality (270 dpi) LCD display, 100% coverage
    * Direct HDMI output
    * ISO 200-3200 (ISO 100-6400 expanded range)
    * CF Type I/II and MS slots
    * Magnesium Alloy body and rubber seals for dust and moisture resistance
    * AF micro adjustment
    * $2699.99 body price

Sony Alpha A850 is identical to A900  except for:
    *  3 frames per second continuous mode (5 fps in A900)
    * 98% viewfinder coverage (100% in A900)
    * IR remote is optional (comes with A900)
    * $1,999 body price ($2,699 for A900)

What makes A900 and it's close relative A850 so special is the 24 mega-pixel full frame (35mm equivalent) sensor that is combined with in body image stabilization. There are a few other cameras on the market that offer the advantages of full frame (such as Canon 1Ds MK3, Canon 5D MK2, Nikon D3x, Nikon D700), but none of them have the in-body sensor stabilization. One may argue that Canon and Nikon offer optical image stabilization in their lenses, and they would be only partially right as by not all of the lenses offered have that feature. Plus on top of that lenses that do have stabilization (IS - image stabilization in Canon and VR - vibration reduction in Nikon) on average cost $300-$400 more than one without this very useful feature. On Sony - all lenses are stabilized regardless of their age, manufacturer or price. As such - you can have  16mm f2.8 fish-eye stabilized as well as the old, but optically spectacular 600mm f4. And even all the macro, "lens-baby", defocus control lenses are supported! As you can see - with a purchase of a Sony camera - any and all lenses that you may own are upgraded to the latest IS/VR version for free!

Full frame stabilized sensor is not the only special feature of the A900/A850. They also feature magnesium allow bodies, very big and bright viewfinders, dual memory card slots and a lot more.

If we look at specifications and prices on full frame bodies by the three major manufacturers - we will see that A900 competes directly with Canon 5D Mark 2 and Nikon D700. All of them are very different and are made for different purposes.

I'm not going to compare every single feature of each camera, as there are other sites that do that, but I will point out what theses cameras do best in which scenario - which is probably the main reason to pick one camera over the other.

Nature and landscape camera - Canon 5D Mark 2

Canon 5D Mark 2 is the absolute best camera for taking pictures of sea/landscapes and slow moving animals in the wild. With its 21megapixels resolution - it is perfect for capturing high detail normally seen in outdoor images. For example it will excel in producing very sharp, stunning in detail images of colorful foliage in the fall. And at the same time - even if the weather is not cooperating - it's weather sealing against dust and water will ensure that you do get that best shot before it's time to pack up and take cover.

Second major advantage of 5DII is the video capture feature. It's not just a gimmick either, it is a high quality recording powerhouse in a small package. While there is a limit of 12 minutes per recording (limit not of the camera, but file structure used to format memory cards), the quality of the video can be breathtaking. With the modern lenses and shallow depth of field - one can achieve the same visual effects and quality usually reserved for $20,000+ video cameras. In fact - it can be used to film important event moments (think weddings or parties), music videos (usually don't require long un-interrupted sequences) and commercial advertisements (which last anywhere between 10 seconds to a just a few minutes).

The major downside of the Canon 5DII is the auto-focus system. It is known to be sub-par when compared to others in the class and even to cheaper Canon models. It is not very reliable on stationary objects and trying to use it on moving objects is simply frustrating. Combine that with 3.9 frames per second and you will understant why I would not recommend it for sports, some types of social events, pet and children photography.

To sum it up - Canon 5DII is your best choice for outdoors and most types of studio work.

Sports and journalism camera - Nikon D700

Nikon took a different approach toits cheapest full frame offering -D700 features 12 mega-pixel sensor, weather sealed body, built-in flash (something no other full frame body has), digital level indicator, dynamic range booster function, 5 frames per second (8 frames with vertical battery grip), and professional camera support and servicing by Nikon.
Of course D700 has many other features, but these are the ones that stand out when compared to some other bodies.
What makes D700 special is its ability to produce very clean, noise free images at high ISO. In fact, the images are so clean and pleasant that you will be wondering why the flash was included on this Nikon and not on the competitor's cameras. The second stand out feature is the great AF module developed by Nikon. It can track fast moving objects well, has spot on accuracy and reliability with stationary subjects.
As you can see - 5 frames per second, clean high-ISO output, great auto-focus module, magnesium allow body with weather sealing and flash makes this excellent choice for anyone who needs a great travel camera (as journalists do) or those who are into sports and need the ability to crank up ISO and capture moving objects at high frame rate.
To sum it up - Nikon D700 should be on top of your list if you are after a great travel DSLR, don't want to carry separate flash and like low light photography.

Studio and event camera (especially weddings) - Sony A850 and A900.

Sony A850 and A900 have a few great features going for them - they have in-body stabilization, highest in class resolution, 5 frames per second continuous mode (for A900) biggest and brightest viewfinders in their categories, dual memory slots and best menu system. To some this may not sound like much, but that all changes when you take a look through the viewfinder, take a few shots and look at the results. The output from Sony sensors is simply stunning. It is capable of capturing so much detail in such a great dynamic range while being very easy and intuitive to use, that one can not be left unmoved. A900 of course has a few other very strong points - 5 frames per second (at this resolution, only Canon 1Ds3 and Nikon D3x, both $6,000 are comparable) and best viewfinder in the class. At the same timeA850  while with only slightly smaller,  less bright viewfinder and 3 frames per second is the best and cheapest full frame you can buy. At less than $2,000 - nothing can come close to the specs and image quality of A850.
And while the two Sony offerings are slightly different, they do one thing exceptionally well - they produce well saturated, punchy images with amazing skin tones and very broad dynamic range. Both also have Sony's very effective in-body image stabilization system. It automatically stabilizes any and all lenses mounted on the camera - Minolta G / APO, Zeiss, macro, wide angle, fish eye, tele or normal. Try getting that in any other mount. Because of these properties - they should be high on the list of anyone looking for a camera to use for weddings and other similar events. You will be surprised how well it captures the slightest differences in tonality and color. Combined with highest resolution, it is no surprise that Sony A900 and A850 are the best options for any kind of studio work.
Yet, both feature magnesium allow body, moderate weather sealing, dual card slots for higher image capacity and a very intuitive menu interface. In fact it is so easy, you will get used to it faster than you think.

To sume it up - Sony has really dealt a double punch to the competition in the form of A900 and A850. The top of the line A900 can be used for anything starting form motionless subjects in the studio, to sports. A850 on the other hand offers unprecedented resolution, image quality and value at less than $2,000. While it is not the top choice for sports with its 3 frames per second, it is the best and cheapest choice for studio and event photography.

At the end I would like to say that while I personally chose Sony A900, all of these cameras are very capable. Yet, everyone of them has a few features that makes them better suited for a particular purpose. For weather-sealed 21 megapixel Canon 5DII it is nature and outdoors. For 12 mega-pixel Nikon D700 with 8 frames per second it is sports and journalism. For Sony A900/A850 with their built-in image stabilization, superb resolution and dynamic range it is weddings, portraits and studio work. Try them all and pick the one that features your style and type of work.

And at the end the word of caution - do not compare Canon 5DII, Nikon D700, Sony A900 and Sony A850 to APS-C cameras such as Canon 7D, Nikon D300s or Sony A700. Full frame cameras are in completely different league. They are very different technically and often times are aimed at a different kind of photographer. Of course this doesn't mean that one can't take use APS-C Canon 7D for studio work or Nikon D300s for landscapes, but they will not produce the same results as the full frame cameras. To make a simple analogy - you can dig a hole in the dirt with a shovel or with a steel bowl, but shovel is a lot more effective and convenient. The moral of this is to use the right tool for the job. APS-C cameras are in general aimed towards amateur photographers and those who do not require the ultimate level of detail. Except for this difference in the image output - cameras with smaller sensors are equal to full frame in all respects.

I personally buy only from Amazon.com and B&H Photo Video. However, I highly recommend buying from Amazon.com for several reasons - they have one of the best return polices I have ever encountered, most products worth $25 or more ship for free, and you probably won't be charged any tax (depends on your state). All around Amazon.com provides one of the best market places with huge selection. Give them a try and make sure you buy from Amazon directly.