It all depends on you and your life style - hence so many differing replies.
Being a UK "country bumpkin" my area of choice was Lanna and its Provinces of Chiang Mai, Chiang Rai, Phayao and Lampang with their mountains, forests and lakes. I then moved across to Isaan (Khon Kaen Province) with its rural countryside.
Sandy beaches, palm trees, condos, beer bars and prostitutes were of no interest to me. My choice, so no further comment from me.