The killer for using iTerm2 is the ability to drop another split in with Cmd+D/Cmd+Shift+D. That's pretty much the only iTerm2 feature that I use with any level of regularity, but it's awesomely handy when you're working.
Being able to save and restore the window arrangement is also awesome. I keep iTerm2 in full-screen mode and I have it split into 4 terminals. If I need to restart iTerm2, I simply choose Window -> Restore Window Arrangement and my split terminals are restored.
