In terms of grammar, the easiest for me is Chinese, the hardest English I guess
In terms of pronunciation, Japanese is the easiest for me and Chinese is the hardest
The easiest for me is Hebrew,
the hardest is English.
I didn't try Chines or any Asian languages.
The easiest - English
The hardest - Arabic and Chinese
I think Arabic is very difficult, it's full of difficult sounds, the writing system doesn't show the whole word, and the grammar is very irregular, at least for beginners.
Spanish and Catalan might be the easiest ones for me.