Even the high velocity ammo like CCI MiniMags will stay subsonic from the short P22 barrel. The CCI subsonic are a bit oversized and will not chamber well in the 10-22 if it has a match chamber.
I like Winchester Dynapoints as a general purpose std. velocity ammo without being crazy expensive.
Remington Subsonic is horrible ammo, avoid.
PMC Moderators very quiet but too weak to cycle.
Any of the std. velocity loads should work in both.