I voted for Travolta. Maybe Keaton has a better body of work overall -- I don't know -- but Travolta's role in Pulp Fiction is far more memorable than any of Keaton's roles IMO.
Keaton has played Batman, Beetlejuice, and earned an Oscar nomination for Birdman. I remember Travolta from Grease, Saturday Night Fever, and Welcome Back, Kotter . . . but since then mostly Pulp Fiction. The only thing I can remember him from in the the past 10+ years is that O.J. Simpson series. It's a tough call. I'd lean Travolta for his most popular work, but his roles in the past 25 years have been pretty underwhelming.