For Yorkshire, I routinely get high-averaging youth batsmen (60+). This year I have one with an 80+ average and an aggressive style. However high their averages might be, I never let them into the first team immediately. They have to continue in the 2nd team for the major part of the first season to prove they are as good as they seemed when I picked them in the draft. If they continue to do well in the 2nd team, I let them into the first XI around game 13. I also prefer to play them in the county championship, starting with defensive, no matter how aggressive they might be. I usually stay away from playing them in limited over matches, 20-20 is a strict no-no for me in their first couple of years.
This strategy has worked for me so far.