I have 22lr, 45ACP, 308 suppressors.
Your choise of suppressors very dependent on how you will be using it. For the most part the best suppressor for a caliber is the one it was designed for.
But for the sake of argument, lets say you can only get a 308 and you want to use it for 22lr. (Or you have a 308 suppressor mounted on a 5.56x45 AR-15 and want to use a 22lr kit on it.)
The first thing you will notice, is that the gun is barrel heavy. It does effect ballance. It does effect where the bullet hits down range.
The secand thing you will notice is that the 308 has more of a first round pop than a 22lr. This is really no big deal, but should be mentioned.
I didn't find the overall DB difference to be that significant. I think the 308 was louder than the 22lr but to be honest it didn't matter. I now use my 308 on my AR, because it is easier to Quick detach than to switch to the 22lr suppressor.
The third item is that you shouldn't shoot lead in a silencer you can't clean. When you shoot the 22lr it produces a little lead vapor. Over time this will coat the inside of your 308 suppressor. I don't shoot that many 22lr rounds out of my gun. At some point in the future, I will spend the money to clean the suppressor.
I reccomend if you can, buy suppressors specifically for each caliber.
If you can't go with a 9mm suppressor that you can take apart. It will be larger. It will probably be a little louder than the best 22lr suppressors.