An odd thing for me with Dolphin is that when I bring up Google, both the stock browser and xScope can find my location while Dolphin can't. Not a big problem, more surprising.
I have the factory and 2 others installed: Opera and Dolphin HD.
Most of the time, I'm using the factory. It does everything I want. My only gripe is that the user agent is mobile and cannot be changed. If I want to visit a page that has both mobile and desktop versions (such as Yahoo.com), I like using Dolphin because you can set the user agent as desktop and it loads the full version of the page rather than the mobile version.
Now on to Opera. Opera is THE FASTEST to load pages. It's also the smoothest to scroll. The reason it's alot faster is that Opera has their own servers that cache pages. While it has it's advantages, I don't like it when I visit secure pages as my username/password gets stored on Operas servers. And also, some webpages just don't look right on Opera. When I want to read the LA Times, I use Opera because it's so much faster than all others.
if you have no use for extra features then the stock browser will do just fine. Thats all i use, i find that all the other browsers are just bloated with things i dont ever use or need, the stock browser is quick and does everything i need it to. Just my opinion tho..