conquest allows 100% warscore worth of provinces, reconquest 133% you dont even get all the cores back in one war iirc the only con is you dont state it earlier, but it does come ready for stating, and rebel free
For 1.22 and before, conquering Syria was better. Money and forcelimit. Tons of money and force limit, and you don't have to wait ten years for it. Syria isn't big enough for reconquest vs claims on everything to be a big deal, Ottos are better at direct coring anyway, and the AE didn't matter.
Syrian rebels were never a problem. They're accepted culture and true faith. Also, your armies are gonna be nearby for quite a while.
You could go straight from kicking in the Mamluks to eating QQ and releasing Persia - which was worth the wait because it had so much development to reconquest, and its heretic religion/wrong culture. So long as you took Mogostan yourself, anyway.
None of that is true now, though. Vassalizing Syria is the right thing to do, 1.23+.