Bangkok - crowded and polluted as ever, but at least you can get from point A to point B in a reasonable amount of time these days. Thirty years ago there were no expressways, trains or metered taxis. Mayhem.
Chiangmai - nice back then, was staying there for over a year back in 1988-89. No bars, airport only operated during the day and was not set up for international travellers. Wororot market parking was as bad then as it is now.
Pattaya - Sodom-by-the-sea.
Phuket - nice back in the early 80's. Could see the whole of Patong beach in one stretch, not a single hotel on the beach side of the road. Last trip was a couple of months before the tsunami, won't be going back. It's going the way of Pattaya.
Samui - was there late 70's. No airport, but they did have the 'express' ferry from Surat Thani. Bus trip from Haadyai to Surat Thani was interesting, they still had vehicle ferries over some rivers back then and we had an armed escort on board for part of the journey due to the insurgency. Bungalow on the beach (basically just a thatch hut - bathroom/toilet was in a seperate block) was 20 baht/night. Ice came from a local factory and was a standard yellowish colour. Stayed at Bophut beach, not a single soul in sight. Absolutely quiet at night. Went back again years later through the airport and was appalled at the pace of development. Scratched of my 'will visit again' list.
I like the Eastern Seaboard, but Ban Phe (after Rayong) is getting overly developed.
Mae Phim beach is nice, there is a small community of expats similar to the cross-section you'd find in Hua Hin.
Another place further up is Kung Wimarn Beach (Nai Ya Am/Chantaburi) that is getting popular with the locals. You can go for your swim then pay a couple of baht to use the beach shower facilities. Hawker food also available, with one or two restaurant-style places. Rumor has it that many local tv stations make some of their series here. Or at least, used to. 12.6036872, 101.8745448