20 is ideal. 6 mid, 6 attack, 6 defense and 2 goalies.
Ideal for players (and coaches) maybe but not for club directors!
I have noticed 24 was kinda standard for a while but that seems to be more in the 26 range now.
As a side note if your club team has 20, it's most likely not because the club is doing you a favor - it's because that's all that tried out or accepted spots.
