When learning a new language, which language is the easiest and hardest to speak? Which is easiest and hardest to write?

Well as per my modest experience it's all up to your mother tongue ... the process will be easier if the language you are learning has a similar content and -specefically - grammar as your native language which means it should derive -at least- from the same family language. For instance, if you suggest to a regular Chinese person the French or Spanish language it would be impossible for him to digest it, however it took me 2 months to speak Spanish fluently only because my mother tongue is both French and Arabic. Thus, this leads us to a conclusion that there is nothing called hardest or easiest language learning.

I suppose it all depends on where the learner is from. There is no easy to learn language. The easiest language to learn would be one that is similar to your native language. It would be easier to learn a language that uses an alphabet (or most of it) that you already know. If your native language is English it would be easier to learn German than Urdu for example.