It's a matter of taste in that both have features that the other doesn't have (terminal being faster being it's main, but significant one).
As far as I know, in terminal you can't use cmd as meta key, which immediately kills it for me as an emacs user (furthermore in iterm2 you can set it up so that left cmd = meta, right cmd = cmd, which I find very useful).
You sure can (I assume you meant opt), and have been able to since the NeXT days. There are many Emacs users at Apple (look at the Emacs key bindings in the text widgets)
As far as I know, in terminal you can't use cmd as meta key, which immediately kills it for me as an emacs user (furthermore in iterm2 you can set it up so that left cmd = meta, right cmd = cmd, which I find very useful).