My thoughts, and I'm new to suppressors myself.
First, make sure suppressors are legal to own, and are legal to take hogs. I'm not exactly sure of your laws, but they may or may not be classified as "game" animals. Suppressors may or may not be legal to hunt with, the laws may be different on private property or for controlling "nuisance" animals. If you do choose .22, it may or may not be legal for hunting. I can't help you there.
The .22 will be the quietest, even with supersonic ammo. I wouldn't care to shoot mild subsonic ammo at a hog and hope for a clean kill, and even the CCI would be marginal in power. Maybe if you could guarantee head shots at close range, like over a feeder, and ambush them.
Your AR would be the easiest to suppress without alteration assuming the barrel is threaded 1/2 x 28. It will have the power to take a hog with the right ammo. The bullet will still be supersonic and it will be louder than the .22. There's just more gas and blast to suppress. There are .22 AR conversions, too.
If you don't want to alter your AR, I wouldn't recommend buying a stock .308 and going through the trouble of barrel threading, etc. It has plenty 'o power for hogs and a wide selection of bullets appropriate for hunting them.
You might look or ask here also:
http://www.silencertalk.com/forum/
(free) registration required