Never been, but have thought about it. Only problem is I like to travel in September and a place like Thailand tends to get a lot of rain during that month. Chiang Mai is a place I've been interested in, as well as Ubud.
Yeah, those months, SEA is very hot. October to Feb is the rainy season I think?
I would highly reccomend Japan. Fantastic culture, great good, super nice people and just a totally different culture. Really fun.
Singapore in September would be really fun. I am actually going this year. I am going to watch the Formula 1 Grand Prix in September from 20-22. It is hot AF and HUMID af around this time though.
If you have already been to most other contintents, I would reccomend Asia. I have been to every contintent (other than Antarctica) and Asia is the most fun for me, anyway.