Disclaimer: I'm a Washington Husky fan, so I have seen Luck and Locker play a ton. Chances are that one of them could end up on your team next year, so I thought I would join to provide some insight.
Luck is money on anything less than 15 yards. He is very cerebral and is able to identify mismatches, soft spots in coverage, etc. He's fairly accurate, but not Bradford accurate. Any throws over 15 yards he seems to float a lot. He doesn't have a cannon and relies on his receivers to make plays, his mismatches, or for his WRs to be wide open to complete any longer passes. He is a very good scrambler, but not ridiculously fast. I would compare him to Aaron Rodgers scrambling wise. He knows when to do it and is successful when he does usually. One thing that Luck has going for him is one of the best offensive lines in college football. Those guys know what they are doing and are incredibly physical. He is great at managing the game and taking what is given to him. He could come into the NFL and be a solid QB right away, but never a superstar IMO.
Locker is a 2-3 year project IMO. He would be great for a team like the Seahawks who have an established QB that is almost done with his career. Locker has the highest upside of any QB in recent memory though. He can make every single NFL throw you could think of, and make them on the move as well. He's just a freak physically, running a 4.39 this spring at 6-3 230 lbs. An NFL GM that watched him play last year said he was "a bigger, taller, right-handed version of Steve Young." His game will get a lot of complaints from fans who don't know the situation he is in very well because they will site his completion % and his overall record. This is only his 2nd year of his life that he has had a QB coach and has run an offense that isn't a Wing-T or a Spread Option. To make matters worse, the offensive line is horrendous and his WRs drop a ton of easily caught balls. Against ASU, he wasn't given enough time by his O-Line for any play longer than 15 yards to even develop. He also had a few perfect passes that hit his WRs in the facemask and he even played with the flu.
Basically, if both of them come out, I would recommend taking Luck if you want a QB who will help immediately although he will likely stay as a mid-tier NFL QB imo. If you had a QB that could play for a year or two, then I would take Locker. Locker has more upside, but Luck is more of a sure thing. I think NFL teams will see the same thing which is why I believe Luck will go in the top 5 to a team that needs him to play right away and Locker will go somewhere in the middle of the 1st round to a team with an established QB but is in the middle tier.
If you have any questions about either, I could try to answer them. I know Luck pretty well and I have watched Locker since he was in High school so I could answer anything about him.