Which Camera is best for each brand?

Which camera is the best out of these Nikon DSLR camera's?

D3000, D3100 or D5000

and which camera is best out of these Canon DSLR camera's?

Rebel T2i, T1i, XSi, XS

If you take answer from Y. Answers, you are doing yourself a disservice! YOU need to go out and handle each one of these models and look through the viewfinder. You should eliminate at least half of the seven models you list. Then ask your question with "I like to take pictures of such and such, I wear glasses (or not) and any other personal details. Armed with the information you collect, then you can make a more informed decision. Add to that if you are comfortable with your camera, you will automatically take more and consequently better pictures as you explore this fun craft.

Nikon: D3100, no question

Canon: T2i, again, no question

Nikon D3100 and Canon Rebel T2i are the best from those choice.