Firefox 17, Chrome, IE9
Firefox has never given me any problems with any of my sites, but Chrome is running a close second. I tried it a year or so and found it buggy, but I'm currently running with 10 tabs and it's working great. I'm using IE9 (32 bit version) less and less because every time I turn around I run into bugs with it here and other places and it's slower than Firefox and Chrome too. It seems like the more MS "fixes" it, the more broke it gets.