FYI, there's no standard on the 12th floor. Standard (now resort) is low floors, usually facing the parking lot. All higher floors on the MK side (I think 5th and up) are theme park view rooms.
Nothing will top what you described, the perspective of being in MK, in front of the castle. But after you've seen it a few times, you may want to get that little feeling of happy but from the comfort of your room or the lounge. I've seen it from the rooms at CR, BLT, and Villains Lair, all pretty similar. It's nice because that song is awesome, but you can't see the projections on the castle much and the fireworks are not angled right and distant. So I'd say it's good enough for when you don't feel like going through the hassle of exiting MK post-fireworks, you can still get a fireworks fix from BLT/CR.
I'm at the point where I've seen it enough that I'll either go through the hassle to get a good view in-park, or just do something else entirely. But I have seen it A LOT, lol