So, I just downloaded iTerm2. I am using zsh in both the apps. iTerm seems to be faster than Terminal.
What things matter when you have a wrapper application around a shell? I want to use iTerm but I don't know why it would be better?
iTerm2's list of features look pretty nice, but if you don't use any of them it won't make a difference for you. A faster term isn't anything to complain about either.
I think the most valuable thing for me would be the 256 colors for vim and perhaps a few other things that take advantage of having 256 colors.