After I used many of dated terminals, everything from xterm to urxvt (was ok), to more modern ones like termite (this one I liked very minimal), I really appreciated everything about iTerm. The amount of GUI customization is insane, plus you can configure everything about from key bindings to mouse, arrangement, etc etc. I really liked it how it doesn't get in your way. Splits are amazing, it is the only terminal where clipboard has worked perfectly with tmux,zsh,vim/emacs combo out of the box. I was really impressed how little configuration it required.

It's just a really solid app that is constantly updated.

Very fast, beautifully rendered text, tabs/profiles/split screen are well implemented etc.