My problem is I have an old version of OS X and I don't get free upgrades on Safari. Yeah, if I owned a rival OS, I'd get free upgrades. Doesn't make sense to me. Maybe I'd like Safari more if I had a newer version, but alas, I'm cheap.
Camino is for OS X and only works on OS X, but it uses the Gecko rendering engine that Firefox uses. So, Camino is a native port of Firefox for Mac. It's fast (-er than Firefox), smooth, and uses Mac style.
The only problem with Camino is that if you like Firefox extensions and plug-ins, they don't work with Camino. But if you don't use these things, then Camino is better -- uses less memory and works faster in OS X.
I switched to Camino from Firefox when I noticed Firefox running slow and sometimes crashing. Camino doesn't do that for me.