My CZs and Buckmark pistol shoot CCI Standard the best. The Trailside and Smith 41 prefer Eley, and Buckmark rifle shoots Wolf. Still testing out the Marvel 1911 conversion. All of them shoot the CCI standard velocity well, so if I had to pick one round that would be it.
If I'm plinking at cans and such (Marlin 39, Marlin 70PSS, Browning SA) I'll use Federal bulk pack and it seems to work well, but I haven't benched any of those and done the various ammo brand accuracy tests with them.