Here’s a fun fact: most keyboard amps are full-range, flat-response (FRFR) speakers powered by a clean solid-state amp. And most PA systems consist of a mixer that can run multiple sources through a clean solid-state power amp into FRFR speakers. So practically speaking, a keyboard amp is really a “one instrument personal PA system.”
Either way — keyboard amp or PA — can work. However, keep in mind that if you rely on the PA, you are at the mercy of whomever is running the PA and the number of monitor sends and wedges you can access to dial up your own mix. If you have your own keyboard amp onstage, you’ll have total control over what you are hearing, and not be dependent on what you can get through the stage monitors/wedges. And, if you aren’t sure what will be at the venue, definitely bring along a keyboard amp.