Games Played vs. Innings Pitched

[Oxtung]

There has been alot of discussion about why player X hasn't been promoted or why player Y doesn't go straight from AA to MLB. I am trying to determine how quickly top prospects actually move through the minors but can't decide on the best way to judge pitchers. Is it better to look at IP or GS/GP? There are positives to both approaches so I'd like to hear what ya'll think. FYI for hitters I'm using GP instead of PA.