Well, i prefer IE 5.
Heard some bad stuff about IE 5.5... Dunno why, but heck, IE 5 is working so why try and screw that up...
Netscape 4.7 seems to be doing mostly fine. Doesn't support all the java and javascript, but sometimes that's a good thing...
Opera 4.02 is... Well it's faster, but it can't do half the stuff...
Netscape 6... Well they did something wrong. Maybe it's just me, but it crashes quite often (especially when dealing with java,...), it loads slow (even a simple ''new window'' is slow, sometimes popups make it crash too). Also, i've seen several sites saying ''Not compatible with Netscape 6'', for some reason.
On the other hand, even though IE's working best for me, i'd rather support Netscape, since... Well there's no IE for Linux... But Netscape's been supporting Linux since... Well not the start, but not too long after the start either