I've been using Opera as my browser for years, ever since it first came out in the mid 90's. I even paid for it when all other browsers were free. I checked out Firefox through the years and Apple's Safari because it came with my MacBook, but have stuck with Opera primarily because of the speed difference. It's always been the fastest on my computers (PC's and Mac). Recently Google came out with Chrome but as I rarely use Windows anymore, I haven't tried it.
For kicks I downloaded the new Safari 4 (beta) for my MacBook and this sucka FLIES! Some pages load in the blink of an eye. Literally. (I'll come to the Saloon and click the "Show unread posts" link, and not even see the page change. I must have blinked.
Plus it's got a cool interface. Wanna see your history of pages visited? Forget a list of old pages, it's got good sized thumbnail pictures of the pages you can just flick through 'til you find what you're looking for.
But it's the speed. Man, is it fast! In fact I just did something I haven't done for 12 or 13 years...I just went to preferences and changed my default browser to something other than Opera.
Oh, and for those with Windows, there's a Windows version that Apple claims is just as fast. Give it a try.
http://www.apple.com/safari/