Every brand carries an ATF that is Dex II compatible, usually labeled Dexron III or Dexron/Mercon or Dex/Merc, Most offer synthetic and/or high-mileage options, although if you're considering synthetic, I'd just get Subaru HP fluid.
IMO, pick your favorite brand, or shop around for price, and buy any of the options that say Dex II or III on the bottle.