In my personal experience, oh-my-zsh slows down things too much. You're better off just taking whatever you really like about oh-my-zsh and configure it yourself.

This is what I do: https://github.com/bbkane/dotfiles/tree/master/zsh

Works great!

"zsh is just fine, you just need to add a megabyte of scripts on top" is not a good advertisement :)