If forced to choose between the two, it would be Sanchez without a doubt....
However, if I were the Lions....
1) Since it is pretty much a given that they are going to suck again this year and get another top 3 pick, I would take Jason Smith from Baylor with the top pick and wait until next year to get a QB. Sure up the offensive line first, that way your rookie QB won't get killed in his first season.
2) Sam Bradford (more than likely he will enter the draft after this season) and Colt McCoy will both be available in next year's draft, which you could almost be certain to get one of the two with your first pick.
3) Give some thought into taking Aaron Curry with the 1st overall pick and get a good lineman later in the 1st round with their second pick.
4) Don't take the pick. Do like the Vikings did a few years ago, and just don't pick until around 7th or 8th. Doing this will not force you to spend $40 mil guaranteed on a guy that hasn't played a snap in the NFL and that you have questions about. Andre Smith could be available around 7th or 8th, and maybe Brandon Pettigrew with their 2nd pick in the 1st round.
Just my scenarios, the latter of which albeit far fetched, may be the best scenario.