re: Which QB will have a better NFL career, Manziel or McCarron?

That's overblown.
There was the imprecise pass to a wide open Cooper in the LSU game, an underthrown deep ball to Cooper and Bell in the 4th against A&M (both of which resulted in turnovers on the next set of downs), and at least one imprecise deep ball to a wide open Cooper against Notre Dame. Luckily, the Notre Dame game was a blowout.

All 3 interceptions were avoidable and very costly last season. The one in the end zone against Texas A&M cost Alabama a shot to take the lead, and the one in the end zone against Georgia helped put an Alabama victory in jeopardy late.