A replacement for the T3i probably won't be out until the summer, so don't bother waiting for it. Of the three you've listed, the D3100 will be the best in low light/high ISO situations. If I were you, I'd get the T3 or D3100 so you have some money leftover for a nice lens.
But before spending 600 bucks on a camera, go to the library and read some basic photography books - they'll help you get the most out of your camera.
Those cameras you listed are good Entry-Level dSLRs. And it's obvious that the Canon T3i is the best,but it's also the most expensive,and I would suggest you to buy the cheaper t2i or even the t3, and spend more money on lenses,which are really important! The D3100 is good too,I own it!
But I would not suggest buying it,because it doesn't have an AF motor,which is something bad for me,because I have to spend money on more expensive lenses that don't have an AF motor. I just feel like Nikon did this to get more money on the lenses with the naive beginners,and Canon made it easier,i don't know. The Canon-Nikon, which is better thing is not important if you don't feel nice when holding your camera.
For me,it's important to feel natural and comfortable when holding my camera. So it would be the best to go to a store,or someone you know that has a Nikon or Canon,and just try out,what feels better for YOU.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.