One of the South American variants of Spanish, probably Argentinian. And I say that despite not speaking any Spanish.

The language itself is a contact language and heavily influenced by centuries of cohabitation with speakers of Arabic. That simplified a lot of the Indo-European complexities away.

The phonology - the sounds - of the language are clear and predictable and sufficiently different that a non-native speaker and their accent are not too troublesome in comprehension.

The language itself is already a world language, ranking 4th in number of native speakers.

I like the suggestion of Esperanto, which I do personally speak and which has all the advantages above, except already being a world language.