I've stayed at both Trisara and Puri at least a dozen times each including both pavillions and villas. Puri overall is much nicer. Trisara has better accommodations. As others have said, no reason really to stay in a villa. Normally I stay in Pavillion 105 at Amanpuri. It's the nicest.
I would skip FS Koh Samui and FS Tented Camp in Golden Triange.
I prefer The Siam or the Shangrila over the Mandarin.