(Ignoring ace-neutral counts such as HO1 and HO2).

If only one side count was kept along with a Zen or HiLo count, which would it be?

I would think Aces, but is it always true?

With a deficit, black jacks and DDs are more likely.

With a surfeit, busts are more likely.

Am I missing anything?

But what other side counts would be beneficial for Zen? Or any other particular counts?