Love street food and I try them whenever I can! In Asia, Japan and Korea actually don't rank that highly for me. Japan doesn't have much variety and Korea's food, served mostly in orange tents or pojangmacha, are more a side show to the soju drinking.

I would say best is Malaysia, specifically Penang, as it is very much a part of its culture to hang out with friends at night trying out different hawker stands. There is also good variety as it benefits from influence from Malaysian, Chinese, Peranakan and Indian cultures. Bangkok is also good for its variety though quality is not as top notch as Penang.