A .30 cal can is a good place to start with.
Are your .30 cal rifles gas guns or bolt guns?
For accuracy the trend is to stay with thread-on cans.
You can get an adapter to run the .30 cal can on the 5.56 rifles (staying with thread-on can)
If you want, to QD the 5.56 later with another can that could be one way to go.
I have no experience with Griffin cans; iirc reading they are decent cans.
Do know that running full power ammo off gas guns .30 cal or 5.56 using full size cans; it is still loud and not hearing safe. Wear PPE.
On a bolt gun in the open, a full size can using full power ammo seems easier on the ears (probably still not really hearing safe, still wear PPE).
My first .30 can was an AAC Cyclone to run on everything; no regrets.
Take a look see at one of your neighbors, Liberty Suppressors. Good people.
eta: Get a .22LR can also!