Roberts did average 13/10/3 in 5 starts last year. He also showed the ability to hit the 3 and make foul shots.
He is somewhat "proven" whereas Jackson hasn't done anything in the league yet, obviously.
If you trade GV, he could be the guy you let backup Holiday while Rivers backs up Gordon. That way, you can showcase Roberts ability a little more. If he is a for real NBA player, he can prove it and that's another trade asset we have. We have a lot of flexibility there.