Ok this is probably a question that's asked a lot, but I am in the market for buying a camera and I can't really find any differences other than the fold out screen. The quality looks the same to me.
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quality is the same essentially. flip out screen is nice though. I think the video button might be in a different place though, but not positive...that may have changed with the t4i. The t4i is a good step up, touch screen and automatic focus in video...real nice.
They have pretty much the same quality. Flip out screen is awesome for shooting video (I have a t4i and have worked with a t3i and t2i) so if you will be mostly doing pics I would get the t2i but if you will be doing mostly video then the t3i. Basically its only if you want a flip out screen.
I actually just picked up a T2i for video. I don't need the articulating screen, because it's just not really useful for most of the things I do. If I really want to monitor my shot, I have an external monitor for that.