What do your friends have? That's what made my decision. My friends shoot canon so I got canon, mainly because I can use/test/try/borrow their lenses.

Mostly focus on glass. Then body features. If you go with canon avoid rebel as the bodies are plastic. Get at least a 50d or 7d. If you want to get go full frame and buy a 5d3. (Hell I might sell my entire lineup for the right price)