1. Ratings
2. Stats
People disagree on the below, but in my opinion, the importance of ratings go in the below order. You can try to backwards engineer how the ratings equate to stats, but I would advise that if you try doing that, make sure you use guys that have played ten seasons and have had consistent play time. Don't let the platoon hitter or specialist pitcher fool you and don't be fooled by small sample size.
Pitcher. Obviously the difference between a high innings guy and a low innings guy is huge, but performance ratings are in order below.
1. R split
2. L split
3. Control and P1
4. Ground ball rating and having at least one other pitch with a 60+ rating
5. I don't even evaluate velocity. I ignore it
Hitting
1. R split
2. Power
3. Eye
4. L split
5. Contact
Fielding depends on position. Ideally you want players that over field the position at every spot. As pray4pro mentioned, defense has a HUGE effect on pitching performance.