OEM or Wix. Wix has plastic end caps with o-ring seals, OEM (Mahle) uses fiber end caps that crush for seal. Both are good. And, last I checked, the only ones available.
NAPA auto also sells the Wix versions under their NAPA Gold line. They have plastic end caps with o-rings and come with a new o-ring for the housing and a crush washer. Part # FIL 100237, $12.50