They all have their downsides, and advantages.
Firefox isn't very native, not quite as good as it's PC counterpart, but add-ons really do make this a great browser despite that.
Camino, I change my mind often on it. I love how native it is, but the lack of features is a big turn off.
Most my experience from Safari is from the Panther version, which sucks with it's outdated Webkit.. and also Safari 3 on Windows.. so I wont really comment on it.
Opera is full of features, but in the end it falls short of add-ons that Firefox has. Also a lot of annoyers like having to-reinstall after updates.. etc.
Overall I like Firefox for it's add-ons. A nice skin, and optimized form-widget build and it's native enough for me.