Hi,
We usually go between Christmas/New years. The express lines have never been too bad from what we have experienced . I would say anywhere between a few minutes - 15/20 minutes max. I remember some "normal" line wait times were 90-120 minutes !!! The parks were packed and the resorts were at FULL capacity, but the express lines were VERY managable. The longest lines we saw were for cat in the hat ( because it seems it is always breaking down), Dr. Doom (because of the very limited capacity), and show type rides ( just the nature of these type of rides) . All of the big coasters were 10/15 minutes max,........ standby on Mummy was 120 minutes, we went on a few times within an hr, with wait times approx 10 minutes. Spidey was always walk-on, and JP.
Our normal annual routine is to do Universal DURING the "big week", and stay on site for express line. Unfortunately, we are stuck paying the VERY high holiday rates.........BUT........it is a VERY stress free week.......sleep in, swim, and do the parks at OUR leisure, because of FOTL. Then we do WDW, after The Christmas/New years rush. WDW is much more managable AFTER New years, and the rates go way down after the new years for WDW.
This year we are doing a split stay HRH/PBH 12/26- 1/2, then we are going to WDW.....ASM Family Suite untill 1/13. I am more worried about the WDW crowds AFTER the holidays then the Universal crowds DURING the holiday.
Just a tip/word of warning...........
We went to US for the New/Years Bash a couple of years ago........NEVER again! It was just SCARY, how many people were there! The parks and citywalk. I remember the club level to citywalk was packed FULL, but the escalator was still loaded with people going up.........it was mayhem. There was nowhere for all the people to get off/go........finally someone smart, hit the emergency stop!!! We got out of there before 12:00, fearing we would be trampled/mobbed to death when everyone was leaving. We went back the room early, and watched the fireworks from the beach of RPR..........much more enjoyable for us.
Go for it.........as long as you are staying on-site, you will have a nice time.........although many people will be a little mad at you as you breeze past them in the express line!
HTH...........Syndrome