Chrome is a light, sleek browser with all the speed you could ask for. Firefox is a massive program with an incredible, powerful range of features and plugins. I'm using Chrome right now, but I tend to use Firefox to play any flash video/shockwave apps. I also use firefox for any secure transactions, as chrome seems to have issues with a lot of secure certificates.
Which is better? They both have their uses.
Oh yeah, and Internet Explorer has one use as well: if you're running a 64-bit version of windows, it has terrible 32-bit emulation, and thus any browser other than IE64 runs like shit under it.