First of all we need to exclude the crews that don't want to conquer anything
- Strawhats Pirates
- Red Hair Pirates
- Whitebeard Pirates
- Kuja Pirates
Then we have the crews we are not sure if they want to conquer or not
- Cross Guild
- Blackbeard Pirates
- Kid Pirates
- Heart Pirates
And finally we have the crews we are sure they want to conquer
- Blackbeard Pirates
- Beast Pirates
- Big Mom Pirates
- Donquixote Pirates
- Germa Family
I would only join the ones the for sure wants to conquer.
From those I would only ally BM Pirates if I marriage one of her daughters. Even that I'm not that tall I would choose Gallette. If that is a possibility then I would join BM pirates for sure. Not only I would marry a beautiful and hot woman but also her family is strong and has a huge army. Also BM and Cracker can make a big army with their DF abilities. And they have good connections around the world to get some info(maybe the best we've seeing in the series).
Beast Pirates are a bunch of maniacs. Impossible to have any plan with those morons.
Blackbeard Pirates is a good one but don't have the whole infrastructure as BM pirates.
Germa Family is too weak both in strength and to get info.
Donquixote Pirates is good too. They are not strong but they rule underworld(that said I would give them better info wire than BM pirates) and Doffy has connection to Tenryuubito so he can kind of use CP-0 in his favor. Would be my choice if I couldn't marry BM's daughter.
To sum up, I would join BM by marrying one of her daughters(has to be Gallette or another one that I think it is beauty) otherwise I would join Donquixote Pirates and for last Blackbeard Pirates. If I couldn't join any of that I would quit dominating the world.
