I'm fond of Opera, but I've found too many (presumably incorrectly-coded, although that matters little in the real world) pages that Opera doesn't get along well with for me to be able to use it as my primary browser without a fallback. And if I'm using a fallback (in this case, Firefox), then there's a case to be made for just using that as my primary.
That being said though, I do like Opera...
That being said though, I do like Opera...