Good Question! We have not been to either however heard that the HK one is a bit on the small side however they are expanding. We plan on doing all of the Asia Disneyland's in 2016 starting with Shanghai, then to Hong Kong and finally doing Tokyo.
I recently listened to a WDWToday podcast that was bascally a trip report for both Hong Kong and Tokyo. From listening to that, if it were my choice I'd go with Tokyo because it has two parks. DisneySea sounds phenomenal.
