Custom games that improve overall skill

What's up all?

What are the best custom games for improving one's overall skill?

I've been playing Marine Arena, and I can honestly say that it has helped me feel more comfortable microing a large army; so I wonder if anyone else knows any custom games that help develop skills that ultimately translate into better performance during normal games?

 

Unit test map.

 

If I were you I'd just hop on and play some Phantom. Always pick slayer that way you're always fighting against the odds when a big bad phantom send a force of superior forces to kill ya. 1wEZS