Chinese is defintely going to be the hardest. I'm learning both Korean and Japanese. I just started Japanese but I've known Korean for a while now. Koreans alphabet was easy to learn. But learning the grammar and formalities is tough, especially at first. Now, the Japanese alphabet is super hard. There's hiragana and katagana. Then there's kanji. They use more chinese symbols than Korean does. So it's really hard to remember everything but I think that forming sentences in Japanese is a lot easier than Korean - WAY less conjugation, if that makes sense. As far as I know (I'll romanize):
Japanese 'i love you': aishitaru
Korean 'I love you':
who are you talking to? someone younger than you or your best friend or significant other? sarang
maybe just a tiny bit more formal to someone close? saranghae
talking to someone you need to show a little more respect to? saranghaeyo
talking to someone you need to show a great respect to? saranghabnida
I'm sure there are formalities in Japanese but I'm married to a half-japanese guy and he says they rarely matter. Korean revolves around the utmost conjugation and formality.