Esperanto, Ido, Indonesian, or Afrikaans.

Esperanto. Logical. Clear. Easy.

I've heard good things about Indonesian/Malay. It probably helps it was a regional lingua franca for a long time.

English was legit the best choice in Europe - analytic, with vocabulary drawn from a couple major families, and (almost) no grammatical gender. If only we could unfuck the orthography...

Globasa. A constructed language, but with most world language families represented, and a process that ensures new words meet a few other good criteria.

Barring that, toki pona.

Lojban, or Toki Pona for shits and giggles.

French, we could all be a little more french when keeping our leaders on a leash

Sanskrit.

Esperanto. It's an artificial language designed to be easy to learn and communicate in. Although it's worth noting that there are esperanto dialects and speakers of one don't necessarily understand speakers of another.

Dutch, but only because I'm tired of Dutch people telling me I really shouldn't have bothered when they find out I learned to speak Dutch.

I just like learning different languages because it lit|really provides new frameworks of understanding for me, goddamn.

Esperanto! Yes, there are better conlangs, yes, it's eurocentric, and yes, there are ways to improve it or even come up with something better. But it has a cool history, it's tied to socialist movements and anarchist movements, it is fairly easy to learn (especially for speakers of European languages), it's grammar is super simple, it uses a system of root words and affixes that make me think of Legos, and it has real, native speakers already, meaning it is a living language that has changed over time, and is fully capable of being used exclusively to communicate efficiently.

Plus, the fascists fucking hate it

Lojban for now
Certainly not Esperanto

1. Lojban like Esperanto has been created to be a neutral lingua franca.
2. I've heard that it's a logical language that tries to do away with ambiguity and that sounds interesting to me.
3. Esperanto feels like a language made for the EU rather than the world and so do all Esperanto look-a-likes.
4. Lojban sounds like a cross between Romansh and a lost native American language. Not good compared to my two favorite sounding languages, Japanese and French, but at least more neutral than Esperanto. Esperanto sounds Spanish and Interlingua sounds like an Italian that thought that Esperanto should sound Italian and I don't like how either of those two languages sound.

Chinese, Korean, Vietnamese, and Japanese are totally unrelated languages. Chinese languages are sino-tibetan, Vietnamese is austro-asiatic, Japanese is japonic, and Korean is alone in its own family. Totally unrelated to each other as far as we can trace.

Despite that, they all used to use the same writing system and, shockingly, they were mutually intelligible when written down. In Japanese this method of reading Chinese (without actually knowing Chinese) was called kundoku but I think that the other languages also had ways to read & write Chinese writing with very light translation. Even today, Chinese writing unites the different dialects/languages of China.

My proposed lingua franca is the Chinese writing system. Everybody should keep their own writing systems, but they should also learn to transcribe into Chinese, the only extant written language in which this is really possible.