Obviously I have a personal preference for English if the world were to pick one lingua franca but grammatically with its cases, tenses and progressive forms it's relatively complex to learn, actually.

Please correct me if someone has more experience, especially in Japanese.

Korean is with a few exceptions. Hindi has male and female but only denoted through verb endings. Japanese has no grammatical gender iirc but makes a lot of social distinctions between male and female.

Nice. doesn't know those about Korean and Hindi. Are they also genderless ?

English has a disadvantage of pronunciations being often not mappable to the written form. I blame French for that

Of these three, I guess Hindi is the easiest to learn. Simple alphabet, two tenses, no special characters to know. I guess Korean is a close second. But all of them I'd consider easier to learn than English.

Grammatically I can think of quite a few. Korean, Japanese, and Hindi for example