I use them all. I find my self using Firefox the most so that is what I voted for. I like IE the least, especially now that we've discovered a problem with IE and entering more than 17 lines of text into these edit boxes.

All browsers seem to work well. Firefox has good support for web developers. IE comes installed on Windows machines so is still the most widely used of the bunch. Chrome is nice, some people like it a lot, but I find its minimalist design a little off putting.
When looking at web site code I see the browser that causes programmers the most problems is IE. In other words there is more special purpose code written for IE in order to get things working consistently across all browsers.
So I recommend Firefox and suggest using anything except IE. Since IE is so widely supported that people will write special case code for it you really can't go wrong no matter what you choose. However I'd like Microsoft to write more standards based software so would suggest people who are computer savvy enough to install a different browser do so. They are all free!