I have seen a lot of debate over which Asian language is the hardest: Korean, Japanese, or Chinese. I will start by saying I have no idea since I have only studied Korean myself. But I do know a bit about all three and I will write that down here so maybe you can decide for yourself. I will compare each based on the following categories: writing/ reading, speaking/pronunciation, and grammar.
Reading and Writing
This is one area where I can at least say which one is easiest. Korean is by far the easiest out of the three. It is the only one with an alphabet. This alphabet is strictly phonetic. I can read Korean quite quickly at this point. I may not have any idea what it means, but I know exactly how it sounds. Chinese has a character set with something like 5,000 characters required for fluency. This character set is not phonetic. Looking at a character gives you no indication of how to pronounce it. Japanese uses this same character set in addition to two syllaberies. One is for native words and one is for foreign words. That being said about the character set, it is not as daunting if you are a visual learner. After an initially steep learning curve, it can be pretty easy to learn vocabulary. I have started to learn Hanja(the Korean version of the Chinese character set) and it allows me to pick up new Korean vocabulary very quickly. It is a bit similar to Latin and Greek roots in English.
Speaking and Pronunciation
I would hazard a guess that Chinese is the hardest of the three in this respect. This is because Chinese is tonal. I know it would be the hardest for me because I am not very musically inclined and would have trouble picking out tones. The meaning of words changes depending on the pitch or how stress the end of the word. I knew a guy who lived in China for three years and knew a decent bit of Mandarin. He said he could kind of bullshit his way through the tones and still get his point across. Korean is not tonal(thank goodness for me) but it does have some peculiarities for the English tongue and ear. It has what are known as aspirated and tensed consonants. ‘G’ and ‘k’ sounds come in three varieties, as do ‘d’ and ‘t’, and ‘j’ and ‘ch’ sounds. I find the existence of these similar consonant sounds fascinating since Korean has no ‘f’, ‘v’, or ‘z’ sounds. Also, ‘r’ and ‘l’ are more or less the same sound. That eliminates a lot of consonant sounds. There is also a vowel sound that we just don’t really have in English. It is closest to the sound between the ‘b’ and ‘r’ in brake. Japanese and Korean(not sure about Chinese) also have levels of formality known as honorific forms. Korean has seven and Japanese probably about the same. Vocabulary and verb endings change depending on the age and status of the two people talking.
Of the three, my understanding is that Chinese is the simplest. I’ve heard that the syntax is very easy to grasp and tenses are relatively easy. Korean and Japanese have somewhat similar grammar systems and use a subject-object-verb syntax. For example in English we say I kicked the ball, but in Korean you would say I ball kicked. I have heard that Japanese grammar has been simplified and some of the more obscure verb endings and forms have been phased out. Korean still maintains the grammatical constructions it has been using for the last few hundred years and is probably the hardest of the two.
In conclusion, each language is the hardest in respective categories but they all seem to balance out to me. I know that the DLI(Department of Defense Language Institute) places all three at the CAT IV level, which is the highest and requires 2200 hours of study. I have heard that at one point Korean was going to be placed in a CAT V level all by itself, but as of right now it remains on par with the other two. So if you are considering an Asian language to learn, don’t pick based on difficulty. I think its best to pick the one that lines up with the girls and food you like best.