This is sliding off topic, but I'm not going to care about that, as the sub-topic isn't intrusive.
From each platform that I've used, Mac OS 9, Mac OS X, Unix, Linux, Windows 98, Windows NT, Windows 2KP, and Windows XP, There's no doubt in my mind that Internet Explorer was most certainly the worst possible browser. The latest version of Netscape Communicator being a close second to the worst.
Windows: You would do well to use Firefox. There are the least amount of problems, and programming from most messageboards is rendered perfectly by this browser. Strange inconsistencies on Internet Exlorer, including image rendering and HTML processing seems to be different between each system. I do not know the reason, as all systems I've tested have the same service pack installed. Internet Explorer also has the most security holes.
Mac OS 9: Unfortunately, you're going to need to stick with Internet Explorer or Netscape Navigator/Communicator because neither Firefox nor Safari is available for this system. Since Mac OS 9 is receiving limited support, you should upgrade to Mac OS X.
Mac OS X: Safari being the Mac's most popular browser is probably due to the fact that it handles quite well since the previous versions. Now blocking over 90% of popup windows, Safari is the best possible choice. Firefox is certainly a close second with just as simple of an interface and just as secure. The other browsers, such as Camino, and Omniweb are from Mozilla, but I've not tested these browsers much. Camino is free, and seems to work well. Internet Explorer has eliminated support and will not longer continue producing new versions for this platform. Just as well, since Internet Explorer performs extremely poorly.