I had booked a trip to malaysia a few years ago, more expensive than Thailand but with very nice hotels in KL and Langkawi. Very nice trip, very nice country and great people, but my favourite country will stay Thailand because people and food. A lot of chinese food in Langkawi, they say they have Thai food, but they just add peppers
. Langkawi is more savage as there are less tourists (many from Korea, Singapore, a few from Europe), you can see monkeys and beautiful bidrds on the beach, in the trees and on electric lines.
I didn't visit Penang, but I guess you have more action (Langkawi is very quiet) and Kuala Lumpur is great, more modern than BKK.
It was funny to see how, in a muslim country, they can celebrate christmas, with many trees and decorations in all the supermarkets in KL, x-mas songs in every hotels... I was coming back from the beach or the swimming pool and there was "jingle bells" inside the hotel.... crazy
The hotels are, I think, a bit more expensive, but food is as cheap as in LOS.
as often, you will get the best price if you find some hotels you like on Internet, then call them to deal the price.