Opera is shareware/payware. It's also used on some phones, IIRC. It's got a MDI interface that, apparently, some don't like.
Mozilla is an all-in-one, free, package.
Firefox is a bare-bones, free, browser, based on some of the Mozilla code.

I use Mozilla because it works well for me for browsing. I don't use the add-ons.

[link|http://hotwired.lycos.com/webmonkey/reference/browser_chart/|Here] is a browser comparison from a programming point of view. I don't know of a recent detailed comparison of features, etc. GIYF. :-)

HTH.

Cheers,
Scott.