My favourite Alolan Form would have to be Alolan Marowak, because of it's access to very good physical moves and a STAB recoil move; Flare Blitz, a strong attack that gets it's recoil negated by the user's Hidden Ability; Rock Head. Takes a while to find a Battle Armour Cubone through SOS Chaining, but if you're lucky to have a user that knows Thief, you could nab yourself it's most important Held Item; Thick Club, which gives it colossal physical attack when held.
The only problem I have with Alolan Marowak is the lack of physical STAB moves due to learning them before Cubone's designated evolution level and how profoundly late the Move Relearner is, barring Fire Punch in USUM.
The Fire/Ghost-type combo gives this Pokemon massive improvement over it's Kantonian counterpart, despite the extra weaknesses.
It is also a nice nod to the mother Marowak's spirit in Lavender Town back in Gen I.