As above, I think a lot of it is down to personal preference.
My main PC is running Windows XP, and I run Chrome browser mostly. It renders pages quickly, and rarely crashes. Though I do occasionally find sites that don't work as expected - eg a .tw hardware support site wouldn't start an ftp download of a driver, so I reverted to Internet Explorer 8 (the latest that will run on XP) and it downloaded fine. Likewise I was trying to place an order earlier and Chrome kept claiming my basket was empty, yet it worked fine with Internet Explorer. But IE is much much slower on XP compared to Chrome.
I tried Opera browser, which I use on my Nokia phone. The phone version is great, but I really didn't get on with the PC version.
I've briefly tried Firefox too, found no specific problems but was already used to using Chrome so I'll stay with that for now.
All that said, I notice that IE on Windows 7 and especially on the beta Windows 8 is a lot quicker than earlier versions, even on the same hardware.
I use twitter a fair bit, and out of Opera, IE and Chrome, it is only the latter that doesn't seem to slow down after long periods of use on there.
Ian