90mm not 57mm .....:o)
Depends on what you can find ammo for. Last time I was at Knob Creek, I ran about a dozen rounds through a pal's 57mm M18, and I loved it- much nicer than the Chinese copies I've previously fired. Ammo for the 90mm M67 is really hartd to find [the Ranger battallions were using 84mm Carl Gustaf M2s for a while, having burned up all the 90mm in the bunkers at Crane, and 90mm/M2 ammo being available from the Canadians at BATTUS. But my latest flashy fave is an M40A1 106mm, and there's more reloadable dummy rounds around for it than either the 57 or the 90. And 106 canister is fun and easy!