Browsers are (surprisingly) rather personal things. One man's meat etc. There are plenty of people who rave about Opera, but I think it's awful. I've tried all the main contenders quite extensively, and for me FF stands head and shoulders above the rest for speed and effectiveness.
Mind you, I'm talking about FF in Linux, not Windows. Maybe it is sluggish in Windows, although it surely can't be as sluggish as IE. There is an optimised (for speed) version of FF (the name escapes me at present) which I have used, and it certainly has a lighter, nippier feel, but I've never felt constrained by FF so I stick with that.
Eric