I’m going to go with worse. Kennedy’s assassination was a tragedy, and whenever a nation becomes unstable leadership-wise even for for a while, it gives other nations with evil intentions, insurgents and terrorists opportunities to take advantage (that didn’t happen in this case), but all-in-all the course of history didn’t change much as a result of Kennedy’s death.
However, if Kennedy mishandled the Cuban Missile Crisis, it could very well have resulted in nuclear war between two superpowers. That would have changed the coarse of history significantly—for the worse.