So the one thing to really consider is what rare pitches there are... I don't know if there are any databases out there yet or not. Because you can only learn a pitch one of the other pitchers on your staff knows.
Also I stumbled on it accidentally, but for those that haven't noticed yet... you can have more than 3 training options (there is a near invisible scroll bar). I'm in my 2nd season, just around the 60th game and have 4 different additional pitch options now but all of them are options 4, 5, 6 and 7, so without accidentally scrolling I wouldn't have seen them.
I made this a long time ago either for show 16 or 17... Should still give a general idea of what pitches do.
https://prnt.sc/izh7qs