Despite Billy S's theory about "gripping power" (that's one I've never heard), I tend to like petite, fit providers because, frankly, they're tighter than larger girls. As for "gripping power," how many providers do you visit who've actually bothered to perfect this skill? Every now and again you run across one, but the vast majority?
That said, over the years I've vacillated between girls with large breasts (who tend not to be too petite), and athletically-built petite providers. It depends what I'm in the mood for.
As for a pretty face...I hate to tell you, but there are a lot of pretty faces out there. These days, that and $2 will get you on the subway.