IE6 was a security nightmare, IE7 was fine but super slow with next to no plugins, IE8 didn't add much of anything, but IE9 is pretty sweet and to date has scored highest on malware resistance against Firefox, Chrome, and Safari.
I use IE9, Chrome, and Firefox, since I have different auto-saved google profiles on each browser, and I don't like logging in and logging off all the time.

IE9 is definitely the fastest for flash and java content though.