I guess the good thing if Sagan moved to Movistar would be that he is old and experienced enough to know what's good for him, what works and what doesn't - because Movistar seem to rely on that extremely. You don't seem to get that much scientific up-to-date knowledge there, more "we will see what works, here's your mentor (Alejandro), with time you will learn..." For Sagan that could work. Still, that team is pretty much a disaster to me at the moment, I wouldn't want my favourite rider there.
Of course there's no winning garantie at QS, you don't get amazing just because you are there. But if I had to choose one team, I would go there, I would even endure PL, because to me it seems the most professional one apart from those Dutch/German tyrants.
What does Sagan need at the moment? I think he needs a team where he can pick his moments and prepare properly for his major goals. Enough rest in between.
To be fair Bora did a very good job for him at last year's Tour, they were devoted to him - of course helped a lot by Buchmann's crash/form. Now he gets good support at the Giro again, it's not like that is a team just for Buchmann and Sagan is completely on his own. In the Tour, with neither Schachmann nor Buchmann doing it and maybe Ackermann neither he will again be a/the centrepiece.
So leaving Bora would probably be about the money or long-term perspectives.