I was trying Opera-Mini and it seemed noticeably sluggish on certain Wi-fi networks, but I love how it handles the tabbed browsing. It doesn't have as many options for how to handle new pages and other miscellaneous tweaks, however.
I was using Vanilla Surf for a few days and while I enjoyed the plethora of options and the speed, the tabbed/multiple page browsing experience was too similar to Safari. Also, it kept wanting to minimize my pages to only half of my screen, to which I'd have to keep zooming back in to restore. I'm not sure if this was a feature of a glitch but I could live without it.
It's a bit a of a toss up at the moment, but I think Opera-Mini pulls ahead simply for the tabbing experience.