The 60D and the T3i both use the same sensor and image processor, as well as the same 9 point AF system. So they'll be pretty much the same there.
It comes down to a few things... size. Which do you like better? Burst rate, the 60D is just slightly faster there but really, not much an not enough to make a real difference unless you spray and pray a lot. And the view finder. The 60D's viewfinder has like 1% more coverage and is magnified slightly more. And the 60D is "environmentally sealed" but really, I shot with a Rebel XT and abused the heck out of that camera for about 5 years. Never had a problem with dust getting in there so to me that's just not a big selling point.
I had the choice between the T2i and the 50D a while back. I went with the 50D for a few reasons, the biggest being the burst rate (it's 6.3 FPS). And while I love the 50D, I sometimes wish I'd gotten the T2i instead. Mainly for the size. But that's me and I'm not you, and only you know which one will fit you.