I've seen two proposals happen within HHN, and while it was pretty cool, there is so much going on between the crowds, noise, scare actors , etc. that it may be smarter to find a quiet place to do it rather than right in front of a scare zone. Perhaps somewhere like Central Park before they start loading it up for Marathon of Mayhem shows?
Other ideas that come to mind:
- VIP viewing area at Jimmy Fallon (if a TM can get you up there)
- The lagoon viewpoints at IOA (particularly Port of Entry or Lost Continent). Would look great at sunset I'm sure.
- The harbor of Portofino Bay
- Outside the Studios arches (if you can find a time that's not busy)
- Anywhere in Hogsmeade with the castle (if you're HP fans)
- NY section of the park during the day. Lots of quiet "side streets" if you want it more private, or the main strip for more public.
I'm sure you'll have a great time no matter what you end up doing. Best of luck!