Safety: Japan ranks VERY high on safety. Singapore is also up there. Everywhere else, it depends on where you are and what time of day it is. In countries like Malaysia and Hong Kong, if you apply common sense and keep an eye on your belongings and your surroundings, you'll be fine. ^
Interesting: Depends on what you find interesting! Historical sites abound in Japan. Shopping for local items is always going to be good anywhere, though beware of overpriced tourist trinkets. Shopping in Japan can be VERY expensive simply because the cost of living there is expensive, but if you set yourself a strict budget you'll be fine.
Staying in a nice place: Great hotels everywhere, and here's where you'll get a better bargain in less-developed countries.
A factor you might want to think about is the language barrier. Japanese are notoriously bad at English. If you're lucky people will try very hard to help you, and they will try very hard to dig up the English they've learned, but don't expect everyone to be able to communicate (even if they want to help). Tourism offices are staffed by people who don't fear English-speakers, but on the street you may have shopkeepers scared of you because they can't communicate and are too embarrassed to ask for help. This can be overcome with a friend who might be happy to be your guide in exchange for meals and transport. (I did this for some friends of my mother who came to Japan but couldn't speak a word of Japanese, and weren't that good with English either. They paid for all my train fares and meals, I showed them the best places to eat and shop, brought them to some tourism spots, and we all had a great time.)
Countries where English tends not to be a problem: Singapore, Malaysia, Hong Kong, Phillippines. I can't speak for Korea, I've never been.