Strome has huge pottential. Great hockey sense, vision, and hands. If he ever does reach his pottential, you could possibly have a franchise center. However pottential and the NHL doesnt always work out. I have fear that his foot speed holds him back from reaching that pottential. Speed really isnt something you can teach.
Mitch Marner would be the safer pick. IMO Marner is almost a lock to be an Elite NHL talent. His speed, hands, IQ make him an electric player. Hes a year younger then Domi and handsdown already better player. Yes he is on the smaller side, however thats not necessarily a pre-requisite to make it in the NHL.
As a leaf fan, i would select Marner at 4/5. Seeing as Mark Hunter is heading the charge this year i cant see the leafs passing on him.