I had the same problem- let me run down what I thought and eventually, let me tell you, I got the Nikon D5100. Let me explain why.
1) The Nikon has continual auto focus during video. The T3i does not. This means that the video will focus by itself while recording. His doesn't work all the time, but it does help a little.
2) It is cheaper. I can't remember the exact figures, but Nikon is definitely cheaper (boh cameras with kit lens or not)
3) The effects on the D5100 can add extra artistic value to both picture an video without editing. May sound cheesy, but it can improve the appeal the video has to others.'mostly the B/W or night Vision one.
4) The Nikon has 11 AF (auto focus) points. The canon T3i has only 9.
Here you go. And yes, Nikon lenses are amazing, for the price. So, I think you should get the Nikon D5100. Hope I helped!