Chrome is the fastest and the most stable. Stable in the fact that it sandboxes each tab so that a crappy website/flash in one tab won't bring the whole browser to a standstill; granted, this uses a bit more resources but can be worth it.
Firefox has the most features by far. Once you start getting used to some of Firefox's extensions you start to become dependent on them (many have mentioned the great AdBlock).
There's no reason to use Safari over Chrome, IMO. It's a tad slower and doesn't have undo-tab-close (a feature I cannot live without) and it's impossible (at least on a Mac, don't use PC Safari that often) to get links to open in a new tab instead of new window by default. (Chrome & Safari both use the same WebKit rendering engine, btw)
Internet Explorer should never ever be used by anyone ever. It is the slowest, most unstable, least standards-compliant, POS. Unless a specific website only works in IE (which is because IE is so wrong sites build themselves around it rather than building it correctly). If you want proof run the Acid3
browser test (info about it and results for each browser here
. (Firefox's IEtab extension is a good way to use IE within Firefox for the odd site that needs IE, btw)
Oops, I forgot Opera. That alone should say enough. (Though the beta's JS engine is very fast)
And Netscape/Mozilla? Netscape basically doesn't even exist anymore, and Firefox was the lightweight, faster successor to Mozilla; "Mozilla" is now known as SeaMonkey. Better off using Firefox and Thunderbird than SeaMonkey, IMO.