ksh, fast. Though my argument used to be that it was more common across platforms that is not so. Still prefer it over bash and the like but that maybe more to do with me loving to type: set -o vi. I tend not to do startup configuration/customisations much as it's easier moving between different computers/enviroments etc. So many times found myself doing some funky changes and alias's and scripts and then feel a little lost on some virgin system elesewere. I also think ksh is faster than bash though thesedays moot. That all said I'm starting to think about writing my own shell, only way to customise. Probably start by hacking around one of the current ones and then play around with few others to get a nice feel to the various approach's and what I like and don't like better into something code quatifiable.

ksh - I feel I may be amongst a small but proud crowd.