Citywalk puts on a pretty cool event called "Eve" that includes live music, all you can eat food, cash bar and pyrotechnics at midnight. This past year included the following venues in the price of admission : CityWalk Plaza & Promenade areas (Bob Marley's – A Tribute to FreedomSM, Pat O'Brien's® Orlando, the groove™, Antojitos Authentic Mexican Food™, CityWalk's Rising Star™, Red Coconut Club™, Plaza Stage and Main Plaza common area).
This past year IOA closed at 10, but Universal was open until 12:30 am had celebrations for New Years. Live music and dancing in the Music Plaza Courtyard, with fireworks and confetti at midnight.
I would choose Universal holiday events versus Disney as Disney does basically nothing for what I like to call party holidays like New Years, St Patricks Day, etc in the parks. Most I've ever seen is green beer in UK in Epcot. Crowds will definitely heavier at UO, but doubt it will be anything like Disney. Have a great time!