If you've already done the 6.5 Grendel, then might as well stay on that 'horse'. It's a good choice. If you were starting all over without a preference, the 6.8 SPC shoots a larger, heavier bullet (on average) and seems to 'hit' harder even if it isn't really producing more foot pounds of energy. Just seems to be the nature of things. Both great choices. Pick the one that makes you happier.
If you are looking for more WALLOP, the .300 HAM'R (from Wilson Combat) pretty much reproduces .30-30 Win ballistics in the AR-15 (for real! Not like the .300 Blackout which never quite gets there...)
I think hogs are underrated for their toughness by some folks. They are at least as 'difficult' to kill as a deer, and probably more so. The traditional 'lung' shot will almost always result in a running pig. The more bullet diameter and bullet energy you can put into them, the better your odds of anchoring them fast. Remember to shoot hogs more 'forward' than you would a deer or elk. Their vitals are more densely crowded a little more anterior on their bodies. Just a tip I picked up on this forum (LRH) that might help.
If you aren't looking to shoot beyond 200 yards, the .350 Legend is another 'bigger bullet' option that can still fit and fire from an AR-15 platform.
As for me, I got a 6.8 SPC and enjoy it because I already shoot .270 Win so I have .277 cal bullets sitting around, which is convenient for me. Hopefully you can figure out what YOU want in your hog gun.
I have a 6.8 spc and a 6.5CM, both would work in my opinion. 6.5 might be overkill sometimes. 6.8 is a pretty neat round, it’s not as widely available but it’s worth taking a hard look at. I’m sure there’ll be users here that know a lot more about it than I do.
Never shot a pig... Shot lots of whitetails and a few Mulies with 6.5 grendel. Im a huge fan, I am having a 6.5 grendel bolt gun built off a stainless tikka action as we speak, should receive it in the next month. I own several calibers for AR 15 and grendel seems to be the one I always grab. Good luck.