Canon vs Nikon Digital Cameras?

My wife is a pro and loves her Nikon D200. But lately we've been wondering if Cannon is a better camera. We've come into some money and she is debating whether or not to switch. She dosn't have many lenses so she could make the switch easily. She mainly deals in Black and white fine art and portraiture. I am looking for an opinion as to what is the best for Black and White Fine art and Portiture. Nikon d200, D2x, D2xs or te Cannon line of Digital SLR's. All opinions are welcomes. I am particularly interested in the opinion of you pro photographers out there.

The Canon vs Nikon debate is similar to Chevy vs Ford,
Coke vs Pepsi, etc..

The best camera for you is the one that you feel most comfortable working with. The layout of the menus/buttons and ergonomics of the body.

Decide which features are most important and how much you want to spend then find comparable models in each brand and try them.

well nikon is the best type of camera for photography like portraiture etc. i have been looking into nikon d50, d80, and d200 and your wife is lucky to have a d200 as they are the best type of slr to work with. i say, keep that one.

With the photography you mentioned, I'm assuming she shoots in low ISOs?
Canon is superior in high ISO performance.
I can look at a picture and can often tell it's been shot on a Nikon because of the noise pattern. Some people like it, I don't. I'm a happy Canon fan. I love my 5D.
In general Canon and Nikon are very close. Anyone that disagrees is misinformed or stubborn.
Spend more of the money on lenses than body, optics will get you more than body will.
I've heard that Nikon optics are better (their best optics versus Canon's best optics), but I can't say from personal experience. Check out
http://luminous-landscape.com
http://dpreview.com
for user reviews.

Okay lets be honest...professionals shoot nikon. For 3 main reasons...F-mount lens, fits all you nikons, nikkor glass is way superior to the glass used in cannon lenses, and even though cannon make some snappy little point & shoots they sould leave the real photography to Nikon. But that just MY opinon.

Actually, none of the previous posts are completely true. If you care about portraiture and don't really care how the file is constructed, then Fuji S3s and S5s are the best for how they render skin tones. As far as the never ending Canon v Nikon debate goes, it just depends on which company released the last camera. Nikon is about to release the Dx3 which will put it ahead of Canon... for the moment.

However, the question really isn't about bodies as much as it as about lenses. For the most part, Canon and Nikon produce lenses of about the same quality. If you want to remain shooting with 35mmm glass and what to increase your quality then Lieca is the way to go.

Nikons have a great flash system thanks to their CLS (good for weddings etc). I agree with the above poster on Canon producing low noise images (good for landscape). And Canon recently developed full frame for their newer DSLRs while Nikons haven't.

since digital slrs don't generally shoot in black and white this kind of a moot point. you can make in-camera adjustments but all that will really do is make your preview images black and white. normally you'd just shoot a great color image and turn it black and white in photoshop.
as far as which camera is better you're really talking personal preference. i like canon but that's because it's what i learned on. i've seen equally quality images from both.
great black and white digital comes from a good initial image, competent use of photoshop, and excellent printing.