I've got a few suppressors (8) now and below are some of my thoughts.
1) Go with a reputable/big name company for your first couple cans. Nothing worse than getting a boutique anything, only to lose support shortly thereafter because the maker closed up shop. SilencerCo, Rugged, Dead Air, SureFire, YHM, Sig, etc should all be looked at, along with many that I'm missing I'm sure. Talk to other can owners (as you're doing here) and see what brands keep popping up.
2) Get a dedicated rimfire can and a .30 cal rifle can as your first two. As cool as shooting a suppressed pistol may look, it's nowhere near as rewarding as shooting a suppressed .300 BLK or a bolt action .22lr (the first time you shoot a bolt action .22 and the firing pin striking the round is louder than the round going off you'll giggle like a schoolgirl). The only place that a pistol can really shines in on an SBR'd rifle. I have an SBR'd CZ Scorpion that is a blast.
A dedicated rimfire can is a must as you'll shoot it
5x more than you'll shoot any of the others. No, I mean that. This is for several reasons:
A) Standard velocity (sub-sonic) ammo is cheap and plentiful.
B) They're relatively cheap; $300-400 gets you a great rimfire can capable of many smaller calibers (including .22lr, .22WMR, .17HMR, 5.7, etc).
C) They're great for introducing new shooters to guns because you can do so without the crack of the bullet and need for hearing protection.
D) Rimfires (especially .22lr) are inherently dirty and you'll want to be able to take apart the can to clean it. Most all rimfire cans these days are user disassembly friendly. This isn't the case with many rifle cans, though more and more are being made that you can take apart. Also, avoid aluminum rimfire cans if you can. Should you ever need to use "the dip" to remove excess leading you'll want stainless or similar. (Please read up on the dip, it's not something I recommend, but is an option if needed).
E) They're universal, almost all threaded rimfires feature 1/2x28 threads, this means you can swap guns/cans at will without needing adaptors.
As for the .30 cal rifle can, you may only have a 5.56 right now, but one of these days you might decide on a .308, or even a .300 BLK upper for your AR. The .30 cal can is more versatile all around, not only that but it will suppress your current AR better than a dedicated 5.56 can. You'll trade a little weight for this versatility, but for my $ it's worth it. Once you have a .30 cal can, if you still want to get a dedicated 5.56 can, knock yourself out, but don't limit yourself on your initial purchase.
3) Once you've knocked out a rimfire and rifle can, you may eventually want a pistol can. And why not, we all want to look like an assassin (note: the only thing I've killed recently was the remaining birthday cake from my daughter's party
). Just like the .30 cal can, you'll want to go with a .45 can for versatilities sake. Some have replaceable end caps that you can swap between 9mm and .45 caps. With any can the closer to the OD of the round your cap is the more gases the can will trap, and as a result you'll see more sound reduction, though just how much of an improvement is debatable.
So those are my thoughts, worth exactly what you paid for them, but some things I hope you'll ponder. Any way you go shooting suppressed is addictive. Once you do it you'll have a hard time going back to a public range with those heathens
who bang away without thinking of those around them.
Depending on where you're at I'll bet there are a couple members here that would gladly meet up with you to discuss and let you try out some cans.