I think Luck over the long term but for the short term RG III will have a bigger impact. However, I'm not sure if RG III will make it through a season without getting injured.
IMO, it's so close it'll come down to who has the better weapons, and who stays healthy. RGIII certainly looked better today, but Luck saw a much better D.
I don't see how RG3 holds up physically. Luck will have a much longer career and, if he is given a decent stable of receivers, he's going to set all kinds of records.