Esperanto isn't intended to be anyone's native language (it's an "international auxiliary language") so that's a weird way to compare speakership.
However I don’t think Esperanto has a shot at becoming a major language.
Pichinglis [1] seems like a good candidate: 70,000 to 100,000 speakers in Equatorial Guinea; formed as a creole from English and various languages of Western Africa, so you should get a high number of cognates similar to Esperanto and a simplified grammar. It might even help you learn other languages of the region faster.
It's probably better to learn a language when you think it'll help you with something you're already planning to do, rather than pick a language and then try to find opportunities to use it. (Also applies to programming languages.)