As much as I like Surovy and how he's progressing with my Pens, I'd have to go the unbiased route and take Taffe here. Taffe is physically more dominating. Surovy is more mature at this point of his development and has better goal-scoring instinct, but I agree that Taffe has a higher upside and will be better in the long run.
I really like Surovy...he IS a goal scorer. But, I don't know about anything after that. Not that it's a terrible thing...score goals, you'll stay in the league a long time. Not a great setup guy...but being a goal scorer himself, he does get guys the puck where he'd want it--in a position with a chance to put it on net.
Taffe seems to be a better all around player, better setup guy, though I don't get to see him as often as Surovy, being in Pittsburgh, so going solely on what I've heard/read. Neither guy is overly physical. Also he has the ability to add some weight, become a bigger player, where I think Surovy is about as big as he'll get.
If they both reach their potential, I'd take Taffe. Surovy might be a 30 goal scorer, but 50-55 points total....Taffe might become a 70 point guy.