Battery life is just barely better on the shift. In my opinion, there's less developer support for the shift. I think this could be because the shift isn't as popular phone as the epic. When i've been out and about, I've seen a few epics but I haven't seen anyone with a shift besides myself. Going from a 4 to a 3.7 inch screen is very noticeable. I hope you have small fingers and your eyesight is good.
I'm not trying to talk you out of it but you should be aware of the negatives. The shift is a great phone but I think it's too small for me.