I would also say Tokyo, no question.
Hong Kong Disneyland is lovely. However there's not that much to do there - I would struggle to spend 2 full days there.
Tokyo Disney just has so much more there, and is on a totally different scale to Hong Kong Disneyland. You could easily spend 2 days in each park, there is so much to see.
The park hours are also likely to be longer in Tokyo.
Be aware that if you get a 2-day pass to Tokyo Disney, then I believe (unless it has changed recently) that you have to pick one of the parks for the first day, and the other park for the second day. You cannot park-hop unless you have a 3+ day pass, and even then you can only parkhop on the 3rd and 4th days.