I like Safari. However, it crashes several times a day and I have never seen another browser that leaks like safari does.
I dislike Firefox. It's way too "PC-ish": cluttered, "unergonomic" (if one can say that about software), and all in just cumbersome and butt-slow.
What I do, is use omniweb. While it has a somewhat large footprint, it doesn't seem to leak as bad as Safari. And that is frankly kind of weird, as it uses the same webkit as Safari.
Often I have Omniweb open for days in a row, and it sits there at 83MB, whereas Safari after 4 hours being open will sit at 345MB. I don't get it. I like how safari is indeed the fastest of the lot (sometimes Omniweb for some reason is), but the leaking, the leaking is a pain in the arse.
Add: Oh, just for comparison, I'm running 10.5.2 on a 2.33GHz MBP with safari 3.0.4 (5523.15)