I use Safari mainly. Adding ClickToFlash was all it took to keep me loyal.
I find it more than fast enough (forum pages here load in an eyeblink), I like the bookmark handling, etc.
I wouldn't use Chrome as it stands now because of privacy/security issues with it (reasons detailed
here). I have SRWare's Iron for testing, but so far haven't seen anything to really make me switch. People who talk about "faster browsing" are generally measuring in milliseconds, which I don't find really compelling (and is potentially just psychological).
In short, I go by the same rule I give to newbies: unless you can show me a compelling reason why you NEED to switch, just stick with Apple's default.