YouCompleteMe will be better than TabNine for API exploration.

TabNine will be more reliable (it will work correctly with malformed, ill-typed, or half-written code) and it can find patterns in your code, like you can see in the pictures on the website.

YouCompleteMe will know the specifics of the language you are in so it will be much better at simple syntax, this will be able to learn how you generally do things and repeated patterns, which usually also will get a good bit of the syntax down.

Hopefully it'd be faster. YouCompleteMe is painfully slow, even after some effort to tweak it.