Most agreeable French resort found by saint (6)
I believe the answer is:
nicest
'most agreeable' is the definition.
(I've seen this before)
'french resort found by saint' is the wordplay.
'french resort' becomes 'nice' (French coastal resort).
'found by' is a charade indicator (letters next to each other).
'saint' becomes 'st' (abbreviation).
'nice'+'st'='NICEST'
(Other definitions for nicest that I've seen before include "Best" , "most appetising" , "Most appealing" , "Most pleasant or fine" , "Most attractive" .)