The week of the Lunar New Year is the busiest of the year. I've been monitoring both HK and Shanghai wait times. in Shanghai, 7DMT go up to 150 mins, Soaring go up to 180 minutes, Tron to 135, Pirates to 75. in Hong Kong, Pooh and Space Mountain go up to 70 minutes, Big Grizzly and Mystic Manor to 45.
The following week, crowd should ease up as the public holiday would be over.
Shanghai is crazy packed and you'll be paying 665 RMB vs 399 RMB on a regular day. Hong Kong crowds have gotten worse as well due to the new bridge. Guest behavior is at its worst so line cutting and pushing/shoving are common. This year I went to HKDL the first two days and saw one kid peeing in public on Chinese New Year day and two on the second. A lot of other things in the city also shut down during these times so I strongly recommend avoiding at least the first 10 days of the New Year. I recommend going a week before or a couple weeks after the holiday (check for when the Annual Passes have been unblocked for at least a week).
Hong Kong crowds would be comparable to Thanksgiving at Disney World and from what I've heard, Shanghai crowds are worse than Christmas at Disney World. If your priority is rides and shows, this is the worst time of the year to visit.
The only reason you should come at this time is if you want to experience some of the special programs. I'm not familiar with Shanghai but in Hong Kong:
1. On Chinese New Year Day, they have a lion dance and special announcement for when the park opens
2. They give out red envelopes with chocolate when you enter the park
3. There's special discounted merchandise at prices better than the Christmas and CM sales
4. They have extra character greetings so it's a good time to see some characters in uncommon locations such as Mickey & Minnie in Fantasy Garden. Last year, Mushu was out for 3 days which was the ONLY time in 2018 that regular guests could meet him. Mulan was also out and she's fairly rare.
5. Comet Cafe and River View Cafe are likely to be open. Comet Cafe is a lot of people's favorite quick service restaurant in the park (including me) and was only open for 3 days in 2018 and is open for 6 days during the Chinese New Year holiday this year. River View Cafe basically only opens during this holiday and busy weekends in the summer.
6. There's more managers out so you have a greater chance of finding a good pins. On the second day, I saw a manager with an LE500 and an LR and I know someone else traded for a PP LE200.