Petterson was better last year. Same offensive production. Petterson finished 9th in PPG while Hughes was right behind him. But Petterson had the defensive edge, finishing 7th in selke voting while Hughes got no consideration for the award.
That being said, Hughes is 3 years younger, and Petterson was nowhere near that level at the same age. I think the evidence points to Hughes having the higher offensive potential, which might be realized as soon as this season.
I personally see Petterson being a selke contender or just on the outside for the duration of his prime, and I can't say the same for Hughes at the moment. But, I believe defensive acumen is overall easier to teach than the higher offensive ceiling that Hughes has. For that reason, im going with Hughes. But it's not an answer I'm overly confident in.