Don't know very much about Luck, but as a Michigan grad I've watched Mallett very closely since his college career began. I still don't know what to make of him as an NFL prospect. He has a Million Dollar Arm, like from another planet kind of arm. His passes literally would shred the gloves of his WRs as a freshman. Can make all the throws an NFL QB needs to make right now. The downside is that he will at times try and make throws that he shouldn't because he has such confidence in his arm and will lead to poor decisions and passes that get picked at critical moments. Generally makes quick decisions and has a really quick release but will try and force things from time to time. Big, strong kid who can take a beating and has not shown to be injury prone. Will need an OL that is strong in pass protection, the comparison to Bledsoe in the pocket is pretty accurate. He actually has decent straight line speed if he needs to take off and run for a guy his size, but doesn't move in the pocket real well. I'm assuming he's matured personally quite a bit since he transferred to Arkansas and seems to have grown up some from what I can tell watching games, but when at Michigan he was not well liked by his teammates. Would openly argue with teammates during games and blame mistakes on them, all captured on national TV (game at Wisconsin his freshman year was a prime example), and you could see teammates staying away from him on the sideline and just shaking their heads at him. Leadership was not his greatest skill and he alienated a lot of people on campus while he was there. He also seriously struggled adjusting to the cold weather in Ann Arbor, so I am not sure how well he would handle life in WNY. He's from Texarcana TX and lived in the south all his life until college.
He's a high risk/reward player. Guy could be a pro bowler and win a lot of rings because he's got a once in a blue moon type of arm, but he could be the next Ryan Leaf if he hasn't gotten all the knucklehead out of his system and get a GM fired. His arm will get him drafted early, no doubt. I don't know if he's the right fit for the Bills though.