I used to use oh-my-zsh but gave up on it after a few months because it took almost 20 seconds to open up a Terminal tab. I switched back to bash with some really basic git completion and was happy enough, enjoying < 2 second opening times.
my tabs open up immediately but it does take a little while to log in, which really is annoying. I think depending on how you configure things you can move where and how often the wait occurs and by disabling certain things, how long it is.
