I have been using Textmate for a couple of years and really like it. I had looked at a few of the others - Coda in particular - but have a natural aversion to “all-in-one packages (like Dreamweaver, for instance 😊 ).
I find auto-complete to be annoying, since it is wrong some percentage of the time. Textmate will insert snippets when you ask it to do so, and allows you to roll your own, which is tremendously useful. One great example specific to EE is the ability to create commonly used CSS shorthand that includes EE variables.
I do not think you can go wrong with any of the suggestion made in this thread - once you become comfortable with whatever you choose, it will be “the best” because you know how to use it!