Law has shown interest in Luffy since the they first met in Sabaody and they have been allied since Punk Hazard meaning he has spent more time with the Straw Hats than his own crew after the timeskip.
Their deal was to take down Doflamingo and Kaido meaning that after Wano they could go their separate ways.
Anyway, if all the Warlords are choosing sides, he’s more likely to be allied with the STRAW HAT PIRATES.
As of now, Jinbe is officially the tenth member of the STRAW HAT PIRATES and the ninth to join.
Doflamingo was allied with Kaido. He was stripped of his positions as a Shichibukai and king after he was defeated by Luffy near the end of the Dressrosa Arc, being arrested alongside most of his crew members by Admiral Fujitora and locked up at Impel Down Level 6. Doflamingo is sure that World Government will kill him but he didn’t seem to mind it, meaning he has a plan.
Here’s my theory: Doflamingo used Jesus Burgess to make a deal with Blackbeard. If he knew he was going down he could have made a deal with Blackbeard since Kaido would have killed him due to the Luffy and Law capturing Caesar Clown and destroying the factories.
What did he offer? THE SECRET TREASURE OF MARY GEOISE. That information is enough for Blackbeard to accept the deal, and Blackbeard has already infiltrated Impel Down before.
Blackbeard sends Aokiji or Shiryu to retrieve Doflamingo since he possesses information to blackmail the Government and is one of the most skilled devil fruit users.
So Doflamingo allies with the BLACKBEARD PIRATES.
This makes sense since he could have one final battle with Law and Law could finally kill him. I think that even Law knows deep down that someone as smart and manipulative as Doflamingo would find a way to escape Impel Down.
What side will he choose? The STRAW HAT PIRATES.
His past plays an important role to why he would choose Luffy.
He was an ambitious pirate who dreamed of becoming Pirate King but after his humiliating defeat to Whitebeard he lost sight of his dreams and ambitions.
After his defeat to Luffy he decided to lock himself away from the outside world and only escaped to kill Whitebeard.
But after the war he seemed adventurous and went to the New World and he was seen reading the news about Luffy in Totto Land.
If all the Warlords are choosing sides he’s more likely to side with Luffy.
Ok there’s nothing to say here. I mean Moria has just 2 options: join Blackbeard or be killed by him and have his devil fruit stolen.
So he is most likely a part of the BLACKBEARD PIRATES.
*Theory by King of beasts kaido