In everyone’s opinion what’s the best move sets for gengar?
They are all useful in their own right. But the must have are Hex + Shadow Ball and Hex + Sludge Bomb. (And obviously Shadow Claw Shadow Ball if possible.)
Gengar is the glass cannon for Ghost and the glass cannon to have for Poison too. Dark Pulse is also a good fast move, but I just TM between them as needed, since fast TMs are plentiful.
Short answer: check out Gengar's page (https://pokemongo.gamepress.gg/pokemon/94) with moveset rankings.
Long answer:
The bests movesets almost always feture Shadow Claw, which is a legacy fast move (we can no longer get it even with a fast TM). I will assume in the following that you just got your Gengar and are looking for what moveset to give him, so I will ignore fast moves.
An interesting thing with Gengar is that it has several useful movesets which will shine in different scenarios.
* In neutral matchups and as a psychic counter (hello Mewtwo), the best moveset is Hex/Shadow Ball. Sucker Punch as a fast move is often acceptable, similar performance, but watch out for the type of your opponent.
* As a poison attacker (useful to counter Fairy and Grass types) and for neutral damage in cloudy weather, Hex/Sludge Bomb is the best moveset. Do not keep Sucker Punch since it is resisted by Fairy types. In cloudy weather, it is interesting in Machamp raids.
* As a fighting attacker, Sucker Punch/Focus Blast is the best moveset. Do not keep Hex here because Normal types resist it and are the main target of Fighting attacks. I tried it Gengar in this scenario and its performance is not great compared to other accessible solutions, especially Machamp. If you have nothing else though, it's serviceable.
From a raid standpoint Hex/Shadow Ball is your best option. A decently large amount of recurring and future raid bosses are weak to ghost which allow Gengar to deal lots of damage in a pretty short amount of time.
Poison's niche is against grass and fairy types. Tangela is the only current boss that warrants poison damage, where Gengar is actually surprisingly solid against Sludge Bomb variants. Beyond that it's hard to justify giving it Sludge Bomb unless you lack the top fire and flying type counters as most other grass types are part poison and the only fairy boss in play is also weak to its ghost attacks.
Focus Blast can be used if you're really hard up on fighting types but I wouldn't recommend it. Machamp is easily obtainable, get yourself a few of them instead.
Against Tyranitar, Gengar is not a good option: all of its fast moves are resisted by Tyranitar.
To get good counters for Tyranitar, check out this page: https://pokemongo.gamepress.gg/tyranitar-duo-raid-guide. And eventually that one, although there is quite a lot of overlapping: https://pokemongo.gamepress.gg/raid-boss-counter/tyranitar-raid-counter-guide. If you don't have a team of 6 of those, try that page: https://pokemongo.gamepress.gg/comprehensive-dps-spreadsheet?pkm=Tyranitar&type1=dark&type2=rock. It lists the best pokemon against Tyranitar, sorted by DPS (you can change the sorting criterion).
Keep in mind that Tyranitar is impossible to defeat alone, you will need at least one partner and both should have excellent teams. To be safe I suggest at least 3 people with decent teams. The more players you can raid win, the highest your winning (and though catching) chances will be.
Good luck!
