Johnson desperately needs a 3, though he's shown a pretty good midrange game this year. He won't be able to out-athlete NBA players like he can in D1. The stretchier a 4 he can become the better his prospects.
Jackson probably has the highest potential but hasn't really shown much assertiveness on the court outside of a few stretches. That may be a system thing, though.
Paige seems mentally like the kind of player you want, but the physical specs just aren't there and the shooting's not really consistent enough to make up for it. I think he'll stick in the league, but as a career backup or 3rd string PG.