vim on the command line, TextWrangler in the UI. I find its nice to have TextWrangler open with my todo.txt and bills.txt files, and is also nice to be able to quickly throw in little hacks / debug code / etc., but for "real editing" vim all the way.
Have you tried using MacVim before? It provides a fairly nice UI for editing files but with the full vim interface/keybindings, and uses all your .vimrc files as well.