The list of tiebreakers is really just way too long to list.
College production does matter, but it's not the only thing that matters. If it were, Tim Tebow would be the first overall pick. The mechanics a player displays usually gives insights into how knowledgeable he is about the position he plays.
Look at it this way:
- DT-A stats are decent, but he displays a wide range of pass rushing moves.
- DT-B stats put NCAA/Madden glitchers to shame, but he uses the same move over and over to beat opposing linemen.
In this case, I'd say that DT-A is the better prospect, since he displays a range of moves that help him change up his game. While he's probably not a perfect prospect, his knowledge of the positions makes his mechanics easier to refine. Coaches can help him with his technique, rather than having to basically teach him the position from the ground up like they would DT-B. In this case, who they play against doesn't even matter, since DT-B won't be able to beat NFL linemen consistently with just a single pass-rushing move.
There are still many more factors, but if you're looking just from on-field performance, what I posted is probably the most important thing you want to look for.