Mandarin of course. i say so not because i am from china. in fact,japanese and korean are from Mandarin,and koreans and japanese used to speak Mandarin.in the 20th century, good koreans and japanese scholars are asked to study Mandarin well. When you have grasped Mandarin,it will be easier for you to learn Japanese. Just like that when you have grasped English,it will be easier for you to learn French.So enjoy your learning Mandarin,sukizo!

Someone says Mandarin is the most language in the world.So I think you should learn Mandarin first.If you are able to learn Mandarin well,any other languages will become easy for you. On the other hand,Japanese and Korean are from Mandarin.In fact,some words in Japanses are still the same in Mandarin. Of course.the most important is what you like better

i don't like japanese!

Mandarin of course. i say so not because i am from china. in fact,japanese and korean are from Mandarin,and koreans and japanese used to speak Mandarin.in the 20th century, good koreans and japanese scholars are asked to study Mandarin well. When you have grasped Mandarin,it will be easier for you to learn Japanese. Just like that when you have grasped English,it will be easier for you to learn French.So enjoy your learning Mandarin,sukizo!

I'd choose the language with a structure close to my native tongue. The more familiarity you get, the better the brain absorbs it. ^^