Deron is a much better run and jump athlete and I believe much stronger. Personally I like players who will be defensive liablilities- I see McCollum that way. If your on-ball D is weak, isn't the opposition going to go at you with guard play? McCollum also like to dribble, dribble and dribble the ball on offense (see Jimmer Fredette). That is a very poor habit for a future role player.
I would rather get Bebe or one of the wings. I just don't see the point guards (small guards) in this draft being very good.