I don’t think best necessarily needs to mean most useful. For example though English, Mandarin, and Spanish are widely spoken they all have their problems, for example the reliance of Chinese on non-phonetic logograms or English’s complete mess when it comes to spelling and vocabulary.
I’ve been learning some Dutch these past few days and have been enjoying it quite a bit. It’s got a lot of the Germanic roots I’m familiar with without the junk and inconsistencies that seem pervasive in English.
Korean also seems like a potentially interesting “objectively good” language to learn since I believe the writing system was invented relatively recently (1950s?) and is phonetic.
All that being said, that’s pretty much all I know about linguistics so I’d love to hear peoples input on language and what they enjoy.