Deciding on an entry level DSLR?

I'm going to be buying my first DSLR soon and I'm stuck between which to pick. I'm in between the Nikon D3100, Canon XTi, and the Nikon D40. If there are any others you could recommend that'd be great! Also: I want to start experimenting with concert photography, which would be the best to start with?

Added (1). I'm also considering the canon rebel t3

DSLRs are considered, 'Professional,' by security staff - most venues won't allow them.

Never buy used without a warranty, and handle a couple of candidates before you commit yourself. Don't close your mind to Pentax or Sony either - Canon and Nikon shout louder, but they aren't necessarily better.

You nave picked one recently replaces camera (D3200 is the newest) and two older ones that you will have to buy used.

Shooting concerts will require a camera that performs well at high ISO settings. The D3200 would be the best entry level camera for that

Before you spend a dime, find out if you can take a fully adjustable camera into the concerts you plan to shoot