This is basically my personal checklist:
- Can I give them ~15 good run-outs a year? If yes, I might them around on the bench and make sure to give them their games.
If not
- Make sure the team will play him as much as possible, obviously am not going to loan players out just to sit on a bench.
- Make sure the player is going to play in a league above or at his standards. I'm not going to send a player to the Serie D when he's clearly too good for it, they need as good a league as possible.
- Obviously if a team is in the same league (or comparable) as me, that team will be at the top of the list if they're going to be starting him.
- Foreign teams playing in European Tournaments are a good choice, too.
- Very much last place, good training facilities. Compared to playing time and playing in a good league, facilities have a relatively small effect on player growth (probably confirmation bias). It's a nice-to-have if you need to choose between two comparable options.