The biggest issue I have with most .30 cans is weight, which plays havoc on POI shift. So long as you're not planning to do a ton of 5.56 rapid fire, I'd look at the Gemtech Sandstorm. That's coming from someone who owns 3 AAC cans.
I have Surefire 762SOCOM-MINI that I use on a 5.56 SBR and a 7.62 AK. When I get a .308 it will be used for that as well. Still trying to figure out if the .300 Koolaid is worth the squeeze.
The Surefire cans are very durable and have a known track record. Durability and minimized POI shift were more important to me than a decibel rating. Also, as the collar portion of the mount can be unlocked the suppressor can be beaten off a gun from the rear if it gets carbon-locked from several days of shooting. AK mags work well for this. I know several folks who's twisty-mount cans have come off with their muzzle devices still firmly attached after they spun off the threads... No bueno.
Look at the saker 7.62. You can change the end cap when you put it on a 5.56 weapon and basically turn it into a 5.56 can. It's an expensive can compared to other 7.62 cans but you're really getting two cans in one if you buy the 5.56 endcap with it.