My current MO for securing the top Suites at chains is very simple.

At Marriott I typically use points for the stay (for a base room) and then (if I want a guaranteed upgrade at time of booking and do not want to chance SNAs or complimentary upgrade at arrival) negotiate with the hotel for a paid upgrade to a signature Suite.

At Hyatt my strategy is the opposite- I typically book the least expensive cash rate and then use 9K points per night to guarantee a Premium Suite.

I have been very successful with this game plan.

I just helped my son use this strategy in Japan where he was able to secure the Designer Suite with Club at Prince Gallery, the Presidential Suite at Suiran, and the Governors Suite at Park Hyatt Tokyo (they have since changed the 9K upgrade to Diplomat Suite)

At boutique hotels the Citi Prestige card was very helpful for lowering Suite costs with the 4th night free benefit. Unfortunately, changes to the card have greatly diminished this benefit.