I'm running W98SE and have tried all of them, but have had problems with each - Firefox takes forever to load and I don't seem to be able to print anything - all I get is a 'System Error' message. It also doesn't open all features in E-Post, Canadian Tire Financial and some Gov't of Can Web-sites.
Opera and IE6 load about 5 times as fast but Opera is not compatible with my Bank [TD], Gov't of Can or E-Post - also, the longer I am on-line [dial-up] the slower Firefox and IE6 seem to get, while Opera seems to maintain about the same conection speed.