I've came to the conclusion that it's a waste to redshirt guys with average potential. They just don't grow much at all, even with decent (45+) work ethic. So RS a good potential is best. Unless you have a guy who is an amazing player right now with decent work ethic. If you just redshirted the guys who had the highest recruit relative value on GUESS, you would be fine.
I honestly don't pay attention to position. But I always RS a QB. Here are my redshirts by position on the team I've turned into a playoff team.
Year 1: RB, WR, DL
Year 2: QB, OL, DL
Year 3: QB, OL, DB
This year: WR, DL, LB