It depends on the show. Typically what they do is give out the "best" tickets first I think, but without evaluating what's actually best. I.e. they might start with the front in a theater with a pretty high stage, and seats a few rows back or in the mezz might actually better (also depending on your preference of seats).
Also, I have a feeling some shows might release some more rush seats close to showtime when they know they won't sell them at face value anymore, and these might be better than what they sold in the morning. But I have no proof this, and would be very risky to speculate on, esp- if you only have a limited number of chanced to try and get tickets.