I've been to 2 happy valleys, beijing and shenzhen, and this year will be at the chengdu and songjang this september, and the fantawild park in wuhu. a place you have to go to just to say "wo-hoo". they have the same feel to them, great theming on the buildings, lots to do, plenty of side shows, theatres. the happy valleys have been around longer and had more time to mature, they have the bigger coasters and are in big cities, Beijing and Shanghai have many international routes, Shenzhen is a stones throw from HongKong, and Chengdu is accessible from Amsterdam on a KLM direct flight.
the fantawild parks, and the second one is in Chongqing where i'm hoping to get to also in september, take a heck of a time to get to them
to get to the Wuhu one, its a train from Shanghai to Nanjing 3 hours, and a train from nanjing to wuhu, another 2 hours, you cant fly there any quicker. Nanjing has other coasters to offer so its worth a making it a 2 day trip.
to get to Chungking, fly into chengdu and then take a 4 hour train to get to Chungking.
for the amount of effort to get there, the parks are not that rewarding, but as i'm working in china and have been to all but 1 park with more than 2 coasters, seriously I have, if you hit the 5 major cities, they are next on my list to visit.