I have been to both CTI and San Souci.

For the AN facilities, San Souci would be my choice. The Island at CTI is nice, but red flag days are common where it is too rough for the boat to take guests out to the Island. I have not been to Couples Negril, but I have heard frequently from those who have been there about the lack of privacy on the nude beach.

A few other observations, there are a lot of stairs at San Souci, but there is a service road down the behind the buildings which can help you avoid a lot of the stairs.

Tower Island is a fun party resort with really good dining options - better dining than CSS in our view. CSS has a much more laid back vibe than CTI in our experience.

Both are nice resorts and you will not really go wrong with either one.