I'm working on a comparison article for MM. Contextualizing Stutzle's production has been among the hardest things, because 1) there aren't a lot of star German players and 2) not many of them played in the DEL during their first draft year.
With Byfield, there are a lot of known qualities from the OHL who have gone on to play in the NHL. His points-per-game ratio and goals-to-points ratio are basically identical to Taylor Hall.
The key difference being that Hall was tied for the league lead in scoring while Byfield was sixth. And Hall had much better numbers (more ice time) playing on the 2010 WJC Canada team.
Canada U20 at eliteprospects.com
That said, I prefer Byfield. The skill and consistency is higher in Stutzle, but Byfield has more to offer and bigger potential.
This will probably sound like a terrible comparison, but personally, I feel Stutzle is a lot like Karl Alzner from the 2007 draft: what you see is what you get. Granted, there's a LOT to like, but if the gap in talent is small, with the gap in potential huge, I'm going to lean for the one with bigger potential.