Personally my criteria would be
.358" bore
7" length
All titanium rated for 300 win mag
Universal rear threading so I choose between the many different manufacturers mounting systems including 3 lug
This would cover 308, 5.56 and 9mm. I wouldn't want any bigger of a bore to cover 45 cal because you'd loose too much suppression when shooting the smaller calibers. I think the Rex MG7 .358 fits almost all my criteria except the titanium part
Edit: the MG7 is only 5.6". They only list it as MG7 k, which is new to me. I've only seen it in the past as MG7. I don't think anything has changed besides the name
The Bushwhacker 46 is the only user serviceable silencer that can be used from rimfire to .45 APC and rifle calibers. If you were going to buy two silencers, a dedicated rimfire silencer and a Hybrid 46M would cover everything.
The hybrid 45 was the first can I bought.
I have used it for everything from 6.5 grendel to 450 bushmaster.
I now have a dedicated rimfire, a dedicated 223/556, a 9/45 pistol, 3 30 cals, and 2 hybrids.
The hybrids are, by far, the most versatile cans I own.