It really all depends on how you see it. There are some easy aspects of the Japanese language, and some easy aspects of the Korean language. Both languages have a similar grammar and word order, and use particles, honorifics, and so on. If your study one language you will definitely have an advantage when learning the other.
Here are things which make Korean easy:
-Spaces between words: Japanese sentences write their characters all together, but not in Korean.
-A phonetic alphabet: The Korean uses a phonetic alphabet so each character represents a sound, while the Japanese uses a complicated syllabary called Kana with a total of 92 characters.
-No need to learn Chinese characters: Japanese uses Kanji, which consists of more than 2000 characters that you have to know to read an average newspaper, and while Korean has its Chinese characters you don't need to learn them.
Here are things which, however, make Korean hard:
-Complicated pronunciation: Korean has many multiple versions of the same consonant, vowel, or diphthong which may sound the same to a non-native speaker and can be difficult to master.
-More complex grammar: Korean has a similar grammar to Japanese, but it's more challenging. For example, Koreans use two particles where Japanese would use one.
Now here are some things which would make the Japanese language easier to learn:
-Simple pronunciation: The only sound that isn't familiar to English speakers is the 'R' which is a flap with the tongue, sort of like an 'l' and the 'fu' which is made without the lips touching.
-Gender and Noun Cases: Japanese Nouns, like English, do not have any gender that you need to memorise. If you are studying Spanish, you know how hard masculine and feminine nouns can be. Also, the nouns don't change in the plural. So 'Nezumi' could mean one mouse or ten!
-Verb conjugation: Japanese verb conjugation is fairly limited and only two tenses exist, and a few other conjugations which you'll have to know, but that's about it.
And finally, here is what will make Japanese hard:
-Kanji: There are about 2000-4000 characters from Chinese that you will have to learn if you wish to master an advanced writing level in Japanese. The complicated part about Kanji is that they are often pronounced differently depending on the context, and you'll just have to know the readings by heart.
-Formality: There are many different ways to say the same thing, but you have to use the right one when you are talking to a certain person. The Keigo (multiple polite forms) of the language is quite difficult to get used to.
-No spaces: Japanese sentences are written without spaces between words.
You will really just need to try your best when you study these languages. They are both beautiful, very mysterious and wonderful languages to know but you have to accept that both of them are hard. I myself am learning Japanese and I really enjoy it, but the choice of whether you will choose Japanese or Korean will be yours. I wish you luck on your studies!