I like Opera the most..
and it was free yesterday
I find it smoother, faster, with better mouse gestures than FF extensions can provide, better tabbed browsing, and MUCH better keyboard navigation (press 'z' to go back, 'x' to go forward)..
the only problem, is it's not AS compatible, and it doesn't have some of the 'toys' firefox has.... occasionally you'll need to load up firefox to continue browsing