Rayong is quiet and has beautiful beaches. Not touristic and you never see youth apart from really young with family. Because of its location it's easy (If you desired) to taxi to Pattaya or get to Bangkok. With it's huge tranquil beach front youll find many photo opportunities if your into that type of thing. Alternatively there's Korat which doesn't have the beaches but makes up for it with many water parks for fishing and eating out, Malls and some amazing markets (save one). It's style is slightly Western with familiar coffee shops littered around the centre with lots of museums, galleries and some fascinating history. There's a few falang but most will be teachers and there's the odd bar that opens until pub hours but no loud music or nightclubs. Korat is said to be the 'new Bangkok' and with its growing development and aeroplane restaurants Korat tries to be unique. I've lived in both and would recommend Rayong for a retiree and Korat for someone whom likes a little hustle bustle and chilling in coffee shops. Good luck