I actually found OM to be more unstable and not as smoothly functioning as the stock browser. It does to a few things better, but overall I prefer stock.
I think it depends what OS you're using.
on my OS7 9900 the Blackberry browser is far better. Blackberry really did their homework with the OS7 browser.
On my OS5 9000 Opera mini is a must
I had the browser close quite often on my old 9700 running OS6 where there was not enough internal memory to load big web pages. I tried the same web page on Mrs. Pete6's 9780 (twice the internal memory) and the web page opened just fine.
On my shiny new 9810 with lots and lots of memory and OS 7.1, I am super impressed. The browser works great. I have never had a crash or a close.
For me Opera is now a thing of the past. I really only used it back in the days of OS 4.5 on my 8310.
I prefer Opera Mini, faster at rendering full web pages and has tab capability. Stock browser on OS7 is a big improvement over OS5 but it occasionally gets stuck and I can't scroll anymore. I wonder if this is a OS version problem. I'm running 7.1.0.258 Also I wish the scroll shortcut keys would be more flexible to configure so that I can match shortcuts on Opera and Crackberry.