I've been using Opera Mobile 11 since it was released. It pretty much demolishes all the competition in both page loading speed and UI speed (2128ms in Sunspider vs 3849ms in Dolphin Mini using the Epic at 1.5ghz).
If you go to an article on Boston's The Big Picture you will see every other browser choke, but Opera seems to render it perfectly with minimal lag and keeps the full resolution images. The stock browser or any other browser it will crash sometimes, if it does not crash then it will scroll very slowly the first time. (example
Another problem with other browsers, they don't render full size high-res images (~3mp+).
Here is an example
, if you zoom to 100% you can easily read what the text underneath the window of the top plane says using Opera Mobile or a desktop browser. Now if you open that image with Boat, Dolphin, xScope, or the default browser you will find it much harder to read.
I believe Opera Mobile is the only browser on Android to utilize GPU acceleration, which probably has a lot to do with the smoothness.
The biggest problem I have with Opera Mobile is the start up time.. I deleted most of my bookmarks and it takes about 1 second to open (down from about 3 seconds), which is still quite a bit longer than the stock browser.
Another issue, sometimes it will say it the page load is complete, yet you can still see things loading on the page (for example, the Boston page above).. Even so, the page will still load nearly as fast as other browsers, that Boston page fully loaded in about 45 seconds in Opera Mobile and 40 seconds in Dolphin Mini (caches cleared on both).. It would be nice to know that the page is still loading.