I genuinely enjoyed the drag-out fight y'all had over these films! So much so, I had to make an account so I could vote for the right film
What was not considered in the discussion, is that both films are presented through the lens of nostalgia. So to say that either film is a genuine or realistic look at either of their respective eras is dismissive of the heightened nostalgic celebration of the eras the films depict.
Grease -at its core- is a celebration of the 50s and so Hairspray of the 60s.
Hairspray is a campy subversion of this nostalgia and that is why it gets my vote.