Literally almost no difference from t4i accept price.
I personally have a t4i and have worked with t2i's and t3i's and I can honestly tell you that the difference in video quality between them all is very minimal. Although I am a fan of the flipout screen for getting high or low angles..
Its simple. If you are on a budget then get the t2i, if you want a flip out screen go for t3i or t4i.