Firefox. No other browser has as much flexibility, and (rather counter intuitively) this means no other browser is as secure as Firefox can be. If I'm on Linux then xombrero, uzbl and similar security enhanced, privacy minded, VI browsers are alternatives.
Firefox was the most hacked browser of 2013. If you wanna search on Bing, go ahead lol. I used Firefox and liked it even worked for them. Then there gamers gate tweet happened