Ace and First-class

Ace adjective - Having or showing exceptional knowledge, experience, or skill in a field of endeavor.

First-class is a synonym for ace in good topic. In some cases you can use "First-class" instead an adjective "Ace", when it comes to topics like excellent.

First-class adjective - Of the very best kind.

Ace is a synonym for first-class in good topic. Sometimes you can use "Ace" instead an adjective phrase "First-class".