The one that works the best with me is MSN Explorer 9.
It's basically like Internet Explorer, only it has a pop-up blocker that actually works and has MSN Messenger features built into it, so it works well. It's something like AOL Explorer, only it's for MSN Messenger. Which, I think that's obvious.
Aside from that, the order I use the browsers in are:
MSN Explorer 9
Opera
Firefox
Internet Explorer 7
Safari
Opera, to me, is the best free downloadable one. It comes with many features in which Firefox doesn't and, for me, it's much more faster than Firefox on my computer. Sadly, some features don't really work on Opera as they do on Firefox and all the other browsers I use.
Firefox, well, nothing needs to be said about that. Everyone else explained why they think Firefox is <the best>.
IE7, well, nothing needs to be said about this one either.
Safari... truly sucks on my computer. It takes decades to load pages and it's font tool is horrible. I do, however, like the ability to resize text boxes. But that's all it's really good for.