Hello Michelle!
So, we have Ohana VS. Kona in a romantic match up, huh? Hmm, let's see ... (cracks knuckles)
Everyone PLEASE keep in mind that what follows are just MY OPINIONS!
I think overall Ohana wins in the romance department. Both restaurants can be loud but Ohana is more closed in and confined where Kona is open to the whole hotel. So, not only do you have whatever noise may be generated by the restaurant but also the noise of everyone walking around upstairs, in the lounge and bar, and throngs of people getting off the monorail and coming in. True that Ohana is basically right around the corner from Kona but it is more closed in and offers a little bit of a buffer.
With Kona there is no buffer, there is no entertainment, and in MY OPINION is a glorified cafe ... which is what it basically is when you look at it.
Now you said that you wanted to eat and then go watch the fireworks on the beach ... now, you could do that but you do also have the option of being able to watch it from Ohana. Try to book a time that is before the fireworks but takes into consideration wait time and back-up. I'd say book a time 1 hour prior to the fireworks ... when you check-in request a table by the front windows ... yes, it is not guaranteed but give them a little extra time and see what they can do ... since it sounds like there is only two of you it shouldn't be a problem as most 2-tables are by the windows anyway.
Once firework time hits, the lights are dimmed and they pipe in the music from the Magic Kingdom and you can sit at your table, eating yummy food, and watching the Wishes fireworks!
As far as being annoyed ... well, that depends on you and where your threshold is ... as everyone is different. FOR EXAMPLE! Some people are annoyed by Lipoa (That is the ukelele woman's name) and the singing ... but for me that adds to the atmosphere and it IS a Hawaiian themed place after-all. On the other hand ...
I HATE HATE HATE when Mommy & Daddy at another table are letting little Johnny or Suzie stare right in your face as you're trying to eat ... THAT raises my blood pressure through the roof!!! Some people tell me it doesn't bother them and say "well, that's just kids" ... no, that is unacceptable ... and I promise you that THEY wouldn't like it if I were to stare in THEIR faces as they were trying to eat! CONTROL YOUR CHILDREN ... even though you are on vacation you are STILL A PARENT ... SO ACT LIKE IT!
Ooo, sorry ... little tangent there!
Anyway, the fact is that Disney World isn't really for romantic couples ... I don't say that as a knock against you ... I just say it because that is how it is. Listen, I LOVE LOVE LOVE Ohana but I wish they'd knock-off the coconut races, limbo, and nonsense like that with the kids at 8 o'clock or so to give a little more adult type atmosphere.
Should you get one of the 2-person window tables you will have a buffer against the kids rather than being right next to the walkway. I think with every restaurant you need to be able to tune a little bit out. Oh, BTW, the ukulele woman is not 100% constant through the night ... she comes on and does a bit for the kids then goes away and they put the slow, quiet, Hawaiian music back on.
ANYWAY ... out of those two I pick Ohana for romance. Better food, more atmosphere, I personally think it's a little quieter and secluded, and you have the bonus of being able to see the fireworks from your table. My family and I LOVE Ohana and go at least once, but usually twice, every vacation ... it's a great place!
I hope this helps ... if you have any questions or concerns about what I went over ... or something I missed PLEASE ask!!! I am always willing to help people with whatever they may need!
Take Care & Be Safe!!!
Frank
Disney DieHard