1. Knuckleball: Far and away the best pitch in the game. It is among the best strikeout pitches, and has one of the best affects on expected FIP. But not only that, it is the only pitch that meaningfully reduces BABIP, and it reduces it so much that expected ERA will be much lower than FIP.
2. Slider: This is a great pitch that has the best affect on a pitcher's Movement and Control in OOTP. It has an average affect on Stuff. One of the top pitches no matter how you look at it.
3. Changeup/Circle Change: I found that these two pitches are identical as far as the OOTP engine is concerned. Only difference is the grip on the ball, the stats will be the same. You can have both of these pitches though and it'll be a double-positive. The Changeup is a strikeout pitch with the best affect on Stuff (along with the Knuckleball). It also has a small penalty to Movement and Control, and a hidden penalty to stolen bases (at least compared to a Fastball). But it's a great pitch for a pitcher's FIP.
4. Knuckle Curve: Unfortunately this pitch doesn't lower BABIP like the regular Knuckleball. But it looks like the most balanced pitch in the game, with solid boosts to all of Stuff, Movement, and Control. A nice pitch to add to a knuckler's arsenal and a top tier pitch on its own.
5. Forkball: Gives a nice boost to Stuff, and neutral on Movement/Control.
6. Curveball: Gives a similar boost to Stuff as the Forkball and Knuckle Curve, but it also gives a small penalty to Movement and Control.
7: Sinker: Not a good strikeout pitch with amongst the lowest boost to Stuff, but it gives the second best boost to Movement and Control after the Slider.
8. Screwball: An odd pitch that gives a good boost to Stuff similar to the Fork/Curve/Knuckle Curve... but it's the most homer and walk prone pitch in the game with the biggest penalty to Movement and Control.
9. Splitter: Nothing stands out about this pitch. Small boost to Stuff, and sometimes a small penalty to Movement and Control.
10. Cutter: Has a weak affect on Stuff like the Sinker, but doesn't have the same benefit to Movement and Control (has a small penalty). Sorry Mariano, but this is the worst pitch in the game. Aside from perhaps the harder to discern following pitch...
N/A. Fastball: I can't rate the generic Fastball because it seems like there's more variables at play with this one. By some of my tests it seems like the worst strikeout pitch in the game. But the Fastball is definitely affected by a pitcher's velocity (faster = better). It's hard to give a definitive ranking to this pitch without extensive testing.
Other Notes
- Oddly, if a pitcher has any rating in the generic Fastball pitch, he will not receive any BABIP benefit from a Knuckleball. From what I see anyway, not sure if it's a visual bug or an intended part of the game engine. So a knuckler should not add a Fastball to his arsenal.
- Remember that the above pitches mostly affect the Stuff rating, and that they're already baked into the displayed STU/MOV/CON ratings. Although the Screwball has the worst dip on pitcher MOV/CON, the affect is still pretty small and definitely offset by the added STU from the pitch. 95% of the time adding more pitches is better.
- Arm slot is interesting, and seems to only affect platoon splits. Submarine/Sidearm/Normal/Over-the-Top <--- From left to right, these arm slots have higher platoon splits. For example, a LHP Submariner will kill LHBs.
- There seems to be some interaction between pitch types, and I can't try out all the combinations. So don't take my list as definitive. There's also probably some more hidden affects of pitches that I'm not aware of.
- These rankings are based on pitches with equal ratings. So even though a Cutter isn't as good as a Slider, a really good Cutter (Mariano) is better than a bad Slider.
EDIT: Forgot to mention my testing was done with a right-handed pitcher. Perhaps the pitch rankings would change for a lefty, i.e. the Slider might not be so high.