I've only used google, but I know theres a bunch of other good ones out there. Just installed a fresh copy of windows, and its time to install a toolbar, so I figured I'd come here and ask first. Only thing that I need for sure is pagerank.
I use groowe, which automatically detects mamma, google, msn, yahoo, ask, alexa, etc. etc. changing automatically the toolbar according the search engine you are visiting, or that in your settings. By the way, this bar is available for both, IE and Firefox, www.groowe.com
None, absolutely none. I value pixels. I only have a pagerank checker, page load timer & adsense earnings counter all in my browser's statusbar.