Knowing SPA airguns, start with some heavier pellets. SPA airguns usually shoot pretty hot (fast) too. And they really benefit from tuning- but you always want to check just inside your crown before shooting. Look for evidence of chatter in the rifling, or burnishing on the lands.H&N Barracudas, JSB Exact Kings MKII Heavies are my top choices in my SPA rifle barrels. Of course I'd try Polymags just because anything that shoot Polymags is FUN. Eun Jins are unlikely to shoot well, but if you have some, try them. Benjamin pellets are always a wise choice to check since they are usually quite inexpensive. Depending on the velocity, I'd be sorely tempted to check Skenco New Boys and Ultrashocks. My SPA barrels like the Skenco offerings and Ultrashocks are brutal on pests.And of course, if the barrel isn't picky, regular JSB exact and air Arms Domes. The JSB Hades appear to be fantastic choice for pesting, and since FX has their Hybrid Slugs, give those a go if you have some coin. Notice I'm not saying stick with any one pellet or two? That because all my SPA barrels seem to shoot a number of pellets well, though they favor heavier pellets. My PP700 pistol is no exception, preferring Beeman Silver Arrows over everything else!However...I'd recommend checking NSA for some slugs, too. Prices are good and if your gun can shoot slugs well, it will open up a whole lot of other doors for shooting.
JSB's are always a good place to start with PCP's. I'd try both weights of them. Failing that, I'd try Kodiaks. I would be shocked if neither of those grouped proper.
My M10 in .22 cal definitely favored the heavier pellets. It loved the JSB Monsters, and the Kodiaks.