Mozilla/Mozilla Firebird.
Opera is ok, but it just didn't seem to suit me. I haven't used version 7.x but I'm happy with Mozilla, and there's no ads.
I would probably be prepared to use Netscape, but why bother when Mozilla is availiable for free? It does everything I want from it, and just needs some work on the initial load time. (In windows, you can have a system tray prog that keeps it open anyway, and that puts it on more even footing with MSIE.)
IE I absolutley hate. It seems every week that there is a new exploit or vulnerability out. Also I don't use Windows, so I'm free of that demon. Patching every hole that is discovered isn't as good as writing secure, organised code in the first place.