Without an external monitor, no swivel screen is a deal breaker for video to me. I grab my 60d or even SX20 for video over my T2i based on swivel screen alone. It just makes it so much easier all of the time.
I've seen examples of the continuous AF with the T4i and STM lenses and its not as impressive in use as it is on paper, BUT it does have it atleast. Understanding it and working within that should be fine (it is not camcorder AF).
If money isn't so much the issue, I would get the T4i. If so, T3i. Personally wouldn't include the T2i as a choice for strictly video use. Magic Lantern hasn't come out for the T4i yet I don't think, but when it does, I would get it immediately
(already available for the T3i)