Every gun is different and what works for one gun doesn't mean it will work on the next gun even if it is the same make and model. Buy an assortment pack in your caliber, and see which pellets shoot the best group at your preferred shooting distance. Pellet induced accuracy problems on lower powered airguns can usually be cured by switching brands or types. Don't use old and oxidized pellets or any deformed examples - discard them immediately. Only use high quality lead pellets from respected manufacturers.
Cheap pellets are false economy.
Airguns do foul barrels but not in the same manner as regular firearms. Instead minute traces of lead and the gun's mechanisms spray lubricants from the compression chamber that deposit in the rifling. This must be carefully removed with a proper airgun barrel cleaning kit. We strongly recommend the Beeman Zip Clean Kit which is a compact flexible rod that won't damage the delicate crown or rifling and it covers all four calibers. Carefully follow the directions for the best results.