Korea for me.
Having also been to Japan before, there a few reasons why I like Korea better.
#1 is cost of living. Tokyo costs way more to live in than Seoul. Koreans like to think Seoul is expensive – it’s not – compared to Tokyo and Shanghai, Seoul is downright reasonable.
#2 is Koreans can speak better English on average than Japanese
#3 is Koreans are easier to read than Japanese. A lot of people put this a strong point of Japanese: that they are more polite, cultured etc. They are actually too polite to a fault. so much so that you can’t really tell what they are thinking. They are too polite to ever say anything directly. You never know whether the girl you are taking on a date is enjoying it or not. Either way she will say she enjoyed it. Whereas with Korean people and Korean girls they will be more direct in telling you what’s on their mind (but not TOO direct like Chinese). That’s the perfect balance I think.
#4 is you are in danger of earthquakes and nuclear radiation in Japan. In Korea you just have to worry about ‘Rocket Man’ but that’s ok – because if he ever does something, all Koreans can die at once and you don’t have to worry about losing any of your loved ones because you will be dead too! yay!