I started on the web with Netscape 3/4.72 (first Internet course I attended and was teacher's favourite); have ended up using IE for banks and other secure sites which have not been checked against anything but IE (except Amazon which works seamlessly with Mozilla and probably everything), and Mozilla for everything else. I like the "Open in new tab" feature, which allows you to browse a site opening several windows one after another, and then close them all with just one click. I also like the fact that the first item on the right click menu is "Open in new window" - IE has a rather redundant "Open", and then next is "Open in new window", which you could do by just clicking, no need for a contextual menu, so why have it up there first?
A2K likes Mozilla too, so that's OK; Composer's almost there as simple web design tool, but is still rather cumbersome, the Mail and Newsgroups module is fine, but doesn't allow you to create identities on top of an existing e-mail account, so you can send *as if* from another (when you went to reply to redirected mail for example).
There are quite a lot of sites now which validate against version 6 onwards of most browsers and under Windows and Linux too. Following site in Spain does, anyhow (list at end of page), and it's going to be easier in future as everyone gets on the standards bandwagon, or will find it increasingly difficult not to:
http://www.alertaantivirus.es
I find Eudora really confusing, though I know lots of people who swear by it; never used Outlook in my life (know lots of people who say it should really be called Lookout); still, the bigger you are, the sooner someone somewhere is going to find a bug.