If you had to pick which one is more important; the ability to block and catch or to throw someone out at 2nd?
I think blocking, catching, and handling the pitchers is more important than throwing down.
I don't think you have a catcher if he can't block, receive, handle pitchers and throw runners out. You need an upgrade at that position.
This is a 12u team, handling pitchers is a rarity but as for the rest of it:
Catcher 1: Can Block and is fast in getting the ball out of his glove, but weak on receiving and throwing runners out and fast pitches are particularly difficult.
Catcher 2: Can receive well, including fast, and throw runners out, but he is weak on blocking and slow behind the plate
Catcher 3: Is medium on blocking, medium on receiving, including fast, and is capable of throwing runners out, but he takes forever to make the decision to throw so not so great on throwing runners out.
The OP talked about which catcher was the "best", and I was trying to figure out what "best" is defined as, i.e what traits are more desirable.