Opera is a bit memory-hungry, but <edit>IMO</edit> it's the best "feature browser" for the phone anyway.

Presto is not weaker than other engines at all; websites designed for other engines may look "simpler" or without visual effects, anyway these are REALLY RARE and show the designer's lack of skill. So your reason that it's incompatible with some sites is not such a huge problem. (Unless it's, e.g, your company's website, which is another story)

And I've never experienced any strange errors with it yet.