I had the Rebel XTi for a few years then upgraded for the 50D.
First time I found a great deal on the XTi + SD1000 on
ebay so I bought it. Used it for a few years then went through this when I was deciding on upgrading. This is where the differences are revealed. Are you planning on building a collection of lenses? because the bodies, while they're more important in DSLR than film, are still a fraction of the cost of lenses (fraction of the cost of one lens, in come cases).
So the question is which style are you more comfortable.. As long as you're comfortable with the body you'll be fine, and honestly some time with either you'll get used to it.
Above all look at the lenses, look at what your longterm goals are because, for me at least, lenses are a long term expendature and investment. Personally I went with Canon because the 50D felt better in my hand and I like the Canon glass selection better. When matched up people may say nikon equivalents are better all along the way but i saw more selection w/Canon and a bigger used market. also, you can place an adapter on Nikon mounts so they work on Canon bodies, not the other way around (if i'm not mistaken).
So look at the specs on the body but think be sure to look past it.. unless you plan on buying a kit and never expanding lenses, then it doesn't really matter and I'd probably go with the pentax tbh having read the above posts.
whichever you pick, enjoy!
