Firefox predominantly. Have used Chrome (on all platforms) but it's...I don't know, there's something about it that doesn't work for me after a little while. Opera is good, but the fonts look horrible in Ubuntu, even with the fixes applied. Safari is a 'meh' experience on windows, but much better in OSX. I've also used Midori on Ubuntu but it crashed a lot. IE in all iterations is a bad joke carried on far too long.
I stick with Firefox because of adblock, no-script and web developer tools. It also 'feels' solid compared to everything else. I've pretty much stopped using Google products, barring their search (which is still the best). My cessation is a mixture of unease at their dominance and just, well, I don't need most of their services.