I'd go with Strome. Arguably more talented offensively, and should be given a prominent role on the Islanders reasonably soon. Couturier will probably take longer to produce, as he's gotta compete with a lot of depth on the Flyers, especially if he stays at C where he'll be up against the likes of Giroux, Briere and Schenn.
I also have a feeling that Strome will end up as a winger... I'd have to go with him though as I tend to be a bit hesitant with players who have the man strength when they are drafted. It just seems to pad their stats a bit as compared to ones putting up similar points with average size and I fear that doesn't translate as well when you get to the NHL.