Firefox
reasons:
add-ons, stability, security, themes. I couldnt live with adblock, flashblock, foxtab, the streaming video downloader add-on who's name i cant remember, and all the other add-ons that i've become so accustomed to over the years i take them for granted.
That and, even if other browsers are somehow "faster", when you're d/ling the content of pages at 2-3MB/s, it would probably be an unnoticeable, milliseconds difference. Honestly, i cant remember the last time i had to sit and wait for a page to load, at least w/o it being due to a delay on the sites end.