I haven't done any grinding other than with files, so I have no experience of hollow grind. How ever, it seems to me that it would be slightly easier to build a sharp transition with hollow grind than with flat grind, and the deeper the curve, the easier (maybe there are other difficulties in deep hollow grinding - it sure looks cool.)
What I'm most impressed with are sharp transitions on shallow angles with flat or even better convex (apple seed) grinds. Even with stones, those are amazingly hard to achieve, and keep crisp and straight.