It is very difficult to say which is "harder to learn" out of two different languages; this is a very subjective term and therefore varies from person to person. While the difficulty aspect of a language is not directly measurable, several aspects that can contribute to overall difficulty to learn are more or less easy to rate. Here are two examples of this:

1) Writing - The amount of characters needed in order to reach an acceptable level of proficiency in each language is very different for Chinese and Japanese. While Japanese does have three character systems, you only need to learn around 2000 characters in order to be able to properly function in Japanese society for an extended period of time (meaning if you are living there and attending school, working, etc). On the other hand, while Chinese only has one character system, you need to learn 4000-5000 characters in order to reach the level of literary proficiency that I described above. This is one very large factor to consider when comparing the difficulties of the two languages.

2) Pronunciation - This is another major factor that sets the two apart. Depending on where you are from and what language you grew up speaking, one language may be easier for you to accurately pronounce than the other one. As a native English speaker that was born and raised in California, USA, I personally find that Japanese is much easier to pronounce than Chinese due to the fact that it is much more similar to the language that I grew up speaking in terms of phonetics and almost all of the sounds that are found in Japanese exist in American English. The two major Japanese sounds that do not exist in American English are the "r" in "dakara" and the "f" in "futari."

All things considered, my opinion is that Japanese is not only easier to learn, but I also think it sounds better and I prefer the writing system over that of Chinese (while many of the characters are shared, the writing systems are drastically different). In addition to this, I find that the culture, technology, and nature that can be found in Japan are all more appealing to me than China's; many of these are featured in The Japan Channel's YouTube videos.

As many others have said, the decision ultimately is up to you. However, I hope that my post has helped you to choose between the two languages as well as the two countries that they are spoken in.