That was a wide open question. I guess it depends on what you'd like to see and do. The best time of year varies a lot too, since the north of Japan can be very cold, while Singapore and Malaysia sit on the equator.

Personally, I enjoyed Borneo (the Malaysian part, not the Indonesian part that has so much civil unrest) a great deal. Very interesting place, very friendly people, great food, great variety from hotel resorts to river tours to ocean trips to beaches.