Arbok

Ah, Arbok. A classic Pokemon from the original 151 with a memorable and threatening design. Too bad the Cobra pokemon is about as threatening in Pokemon Go as the scary face on its hood: purely for show. Arbok has poor ratings in both offense and defense, a typing that has a lot of competition (none of which is truly outstanding), and a largely mediocre moveset. Honestly, there's a severe lack of reasons to justify an investment in Arbok outside of personal love for the species. Either that or just wanting to see a giant cobra coiled on top of your local gym.

Best PvE Offensive Moveset

• Acid should be paired with Gunk Shot to get maximum possible performance out of Arbok on offense
• Bite should be paired with Dark Pulse, though Arbok really isn't even worth a mention as a Dark-type attacker.
• Dragon Tail is a good move on offense, but it doesn't pair well with any of Arbok's charged moves.
• Sludge Wave is strictly inferior to Gunk Shot.
• Acid Spray is objectively terrible on offense.

Best PvE Defensive Moveset

• Dragon Tail is Arbok's best defensive quick move, sporting good power and great coverage.
• Acid and Bite are serviceable on defense, but aren't outstanding by any metric.
• Dark Pulse has good counter-coverage and is a two-bar move, making it the best charged move on Defense.
• Gunk Shot has great power, but Arbok may never get a chance to fire it, and its typing doesn't pair very well with Dragon Tail in the face of steel-types such as Metagross 
• Acid Spray has terrible power, but it is a three-bar move, meaning it could at least do something before Arbok faints?
• Sludge Wave has no business being on Arbok. If you want a poison charge move, Gunk Shot is objectively better.

Dragon Tail sports the best energy generation and damage output among Arbok's fast moves. Bite offers strong Dark-type damage, but has the worst energy generation in the game. Acid is a bad move despite getting STAB, and is generally not recommended.

Dark Pulse costs a moderate amount of energy, and provides coverage that is not only relatively neutral against most Pokemon, but also covers Arbok's weakness to Psychic-types. Sludge Wave benefits from STAB to deal significant damage if unshielded, but costs a lot of energy. Gunk Shot takes it one step further in terms of energy cost and damage output, which is not appealing due to Arbok lacking high energy generation. Acid Spray offers niche plays for baiting shields, with inconsistency being the main drawback. Return could also be an option if Arbok is purified from its shadow variant, but lacks STAB and can't be Super Effective vs anything.