Just fyi, I would not get m43rds personally. The size difference isn't enough to matter for me, it's still not fitting in my jeans pocket so I'll be carrying it around my neck.
The weight difference is often way overhyped as well. Especially since the g3 is one of the heavier m43rds cameras.
And you do lose some image quality because m43rds uses a smaller sensor.
If size and weight are primary concerns, the t3i is fine, though I would personally be more tempted by the t2i which costs less and for the most part just doesn't have the articulating screen - something that could be very useful but when I tried it I found that Canon's really slow autofocus with the screen made it a little useless. (Both cameras use the same sensor.)
Compared to the t3i, the 60d is heavier. And they all use the same sensor. But the 60d, in my opinion, is the best price/performance point if you're looking for a midrange dslr. I really liked it's much faster burst rate (almost 6fps vs the 3fps on the t3i/t2i), much larger raw buffer (16 frame vs 6 frames), bigger grip, better viewfinder...and there were probably some other things. It's main drawback is that it costs a little more and it is a little heavier than the other models.