You're question is kind of hard to answer unless you've experienced both of them enough to understand the learning curve for both ships.
I'll try to put it simply.
Solo + Sloop = "hard" mode
Duo + Sloop = "easy" mode, if you and crewmate know what you're doing.
End up solo + Galleon = Quit and reload solo, or sit and wait for a crew, cause you're b***d if you sail out solo on that ship.
3-4 person crew + Galleon = Really fun and equal playing field with everyone else (If your crew isn't missing all their marbles) OR = a death sentence cause the ship won't operate efficiently without a competent crew.
That's about as round about and basic of an explanation as can be given. You really just gotta play and learn all the mechanics yourself. You'll have to experience the good crews and the bad crews and all of it, before you can decide for yourself what you want to play.
EDIT: I said hard to answer, when I meant there's just a ton of info on both ships that you need to know, in order to make a decision.