At the moment, I am using Mozilla Firefox 3.0.7 (published version) but there is a beta version which is the 3.1 beta 2. I don't really recommend the beta version because it might clash with many of your programmes. Just stick with the launched version of 3.0.7 until now.
I have longed to stick with Internet Explorer 8 RC 1 but I could not do so. This is because the browser is a memory hog for no apparent reason and it slowed down my system. It is bad enough that I am running on a single core CPU, let alone with 2GB of DDR1 memory. It is rather slow but browsers should make way for older CPUs, right? Right now, Opera is trying to do a good job. They are alright but not as user friendly as Firefox. Don't get me wrong, all browsers are similar but it is just a matter of preference. I feel that Firefox is more stable and faster as compared to other browsers. Apple's Safari 4 beta is also not too bad at all but I don't really like the tab buttons. On the whole - Mozilla Firefox is the best!