Prettiness? If it blends in with the native look of the OS, that is "pretty" to me. Safari fails at this. Firefox does not.
Speed? I have a Core i7 idling at 1% CPU all the time, unless I'm doing HD video encoding. Even on my Core2 Duo, I can't remember last time I was CPU-constrained when browsing stuff. Why on earth would I care about speed?
Standards compliance? Firefox is top notch, and while Opera and Safari may go full 100% on ACID3, that is for a spec which is not even finalized and standardized yet. Anyhow, you need to keep MSIE in mind when developing stuff, so this point is pretty moot.
So what do I care for in a browser?
Stability, that it works intuitively, that it's configurable, that it sports a decent feature set, keeping mouse-dependency to a minimum and that most operations apart from link-clicking can be done trough keyboard operations and probably most of all: that it is extendible and that I can add whatever crap I feel I need in a browser. Things like Ubiquity, Firebug, Flashblock, Adblock, Rikaichan, Mousegestures, Greasemonkey, custom dictionaries and Bugmenot.
I pretty much think that the browser should supply me with the core basics, and let me decide from there on what I think a browser should be. If the browser is going to be the "OS of the web and the future", you better believe I want to have a browser which I can make mine.
Edit: Evidently Safari 4 actually sports a somewhat native interface in Windows.