This one is easy, senior year Monte Morris.
If it's about picking the player that had the most positive overall impact, it's Monte every time.
His expected win shares per 40 minutes his senior year was .210. So, if the rest of the players on a team could play at his contribution level you would project to win 105 out of 100 games.
I did vote Niang for this question though.
This team needs proven offense.
His senior year scoring chops are head and shoulders above the other players. A true shooting percentage of 62.5% with a usage rate of 28.7% is filthy.
Also, he would fill more of a position of need (I am a Lipsey fanboy and wouldn't want to see his minutes cut into).
His vocal leadership I think would be better than Monte's too, but if you're looking for intangibles then Hogue's toothpicks and karate kicks trump everyone else.