Everyone above is right. My post isn't arguing their points.
As DonC. Pointed out, a good one can do both, but;
A true air stripper allows the gases to be stripped away (redirection) from the bullets path more so than slow them (Suppressor.)
These gases create a disturbance of the bullets departure. Even if everything is perfectly symmetrical. Though you'll see a stripper works like magic on barrels that weren't perfect to begin with.
In a PCP/SSP/ any airgun, the projectile is pushed out first. Barrels like a Smooth Twist definitely allow the pellet to be first with little to no air passing the projectile, until the seal is passed at skirt of pellet leaving the crown.
It's at the crown which is crucial that a projectile not be blown one way or another off intended path.
I understand the question is "LDC or Stripper." The answer isn't that simple.
I don't need quiet airguns but I sure enjoy them more. A stripper can reduce recoil in a firearm significantly, majorly.
A moderator slows that air and by doing so you will notice a huge increase in back pressure, which isn't true "recoil" Especially if your suppressor isn't matched up for the power. There's also timing.
I timed my Sumatra .25 Rocker1 with a simple plastic bushing taken down in length slowly until POI was the same. With suppressor off or on. Harmonics play a huge part also.
https://youtu.be/OksIysh0eTU
The above video is exactly why a FX liner must be harmonically tuned off you want it optimized. It's also why I choose 0.750" thick barrels.
It's exactly why on a "Big Bore" powerful slug gun, I chose a Scandalous by John Bowman. All 3 Lilja barrels are 32tpi for three full inches of 96 tapered cerakoted threads into a monoblock. Then mill through the block and barrel as one. Add bolt, add cocking lever.
Look at most big bores or any component gun. You don't get 1/8"moa with 420257 cast slugs from something that doesn't have a solid mated barrel.
From "Smarter Every Day."
https://youtu.be/IAR4yTYslkk
Shockwaves are created even by subsonic projectiles:
https://youtu.be/BPwdlEgLn5Q
And folks, please be aware, pellets & slugs aren't like any high speed varmint bullet, or plain lead. These things can be deflected & keep on trucking.
https://youtu.be/F3FkAUbetWU