I have a 2B in his 3rd professional season (20 yrs old) and I was wondering if promoting him to the bigs or leaving him in Double A would be better for his development? He has developed very well in the minors so far but what I've read in the forums has been a mixed bag so far so I was hoping to get some clarity.

If you're in win now mode, or need wins to avoid MWR, then call him up. But games played is more important than the level they play at in my experience. Having said that, the bigs = higher rated coaches = theoretically better development. If you do promote him just be sure that he plays in every game, whether that be as a starter or as a rest or defensive replacement.

I'm fairly certain development is a use it or lose it kind of system. Meaning you can't make up for games missed in a players development process. Every one of my prospects plays in every spring training game, every regular season game and hopefully as many minor league playoff games as possible. I do this by having all my top prospects come in as rest replacements in the 6th inning of every game. This also means they are only getting 250-300 PA and less likely to get injured than if I had them playing as starters. I've never been disappointed with a prospects development using this system.

I also tend to keep my MiL prospects at whatever level my best coach is at, regardless of age. If my best MiL pitching coach is at AAA and my best MiL hitting coach is at AA, the best pitching prospects go to AAA and the best hitting prospects go to AA. I also try to hire hitting coaches and pitching coaches at my bench coach position in the minors too for (potentially?) bigger boosts to those ratings.