Hey, hey, welcome to Flyertalk, Andrew!
Paid stay or award travel? If paying, what is the difference in price? How meaningful is the price difference to you? What kind of hotel do you usually stay in? These are all factors that will help us give you the right advice.
Generally speaking though, even though there is no Regency Club at the Park Hyatt Tokyo, there is no other Hyatt I've ever stayed at that compares to it. If it's award travel, go for the PH without a second thought.