Here's a video I made of my two 30 cal suppressors on a 308 and a 223. FWIW, my dealer has several suppressors and he's of the opinion that if going 30 cal and 223 it's best to just buy a 30 cal can and use it on both and I agree. My 30 cal can is quieter on the 5.56 than his dedicated 5.56 can is, but his Surefire 556 is not in the video.
Just my opinion, but I'm very happy with my 308 suppressor on my 5.56 rifles and you couldn't go wrong doing it that way. You can always buy another can in the future, but it makes alot of sense to get the most flexible/versatile one first.