Personal proposal preference (that has everything to do with how I think proposals should be approached):
Killian and Emma are sitting somewhere innocuous–Granny’s, the library doing research, the Jolly Roger–minding their own business (or maybe it’s post battle and they’re standing over a vanquished foe) and Emma just looks at him and says, “You know, I think we should talk about getting married”. And Killian’s like, “What?” And Emma’s like, “I mean, we’re both in this for the long haul, so I think we need to have that conversation”. And they do, but Killian’s like, “But I get to do the proposing still, right?” And Emma’s like, “Yes. Absolutely. Knock yourself out big guy.” And THEN we as the audience get to witness Emma’s growing sense of anticipation as she waits for Killian to propose. Like, she’s completely in the dark, because Killian likes surprises (and of course he involves Henry), and that excites her because she knows that whatever he comes up with will be amazing.
(Now watch me write fourteen different proposal scenarios, none of which have anything to do with any of this…)