Which to visit : Nara or Kobe

As you said, the distance is not that different, but which is “better” depends on your preference. If you like traditional Japanese places like temples/shrines, then Nara would be the more optimal choice with the Great Buddha at Todaiji, etc. Kobe is more a mix of the old and new, the western and the Japanese. You’ll find a modern port city (shopping mall, Ferris wheel) near the water, and on the hillside you’ll be able to tour the former residences of foreign merchants. And the night view from Mt. Rokko is one of the best in the country.