A couple of times a year for the best part of a decade, I give the various Opera browsers another try, and I always find them to be a complete waste of time, either they're slow, they don't render pages "correctly", or their UI is just a complete mess. I'm sure it's fine in _some_ cases, but for my uses I find it to be horrible when compared with some of the other alternatives.
FWIW - Firefox mobile isn't looking promising, takes too long to start and doesn't seem to accept pages passed to it from many apps to open. I'll stick with DolphinHD until something that is better all-round turns up.
Edit: Hadn't heard of the Miren browser until just now, having a look at it and I'm quite impressed. Might make my primary for a while.