We love Thailand, ds did his scuba course there one Christmas. Of course you get the tsunami anniversary if you go then, very moving. Plenty of markets, culture, nature, beaches, snorkeling, boat trips etc.
Cape Town it's a lovely time of year. Robben island, surfing at Muizenberg, fab cheap wine and food. Going back this Christmas.
Singapore, markets, chinatown, sentosa island, fab street food.
Kathmandu, awesome, loved it. Pollution horrific, the culture, history, white water rafting, elephants, trekking, national parks, flights over Everest.
Bangkok, street markets, shopping food culture, everything and traffic!
India, dehli and Agra, or train journey Jaipur, jodphur, plenty to chose from.
Sorry can't help you chose as we've loved them all. Oh and of course Cairo, Istanbul, Jordan .......