In Kurume, I felt riding the bus got me quicker to places. The trains are good too but for most places it’s easier via bus and they come requently and very often it wouldn’t be very packed at all. Because, unlike bigger towns or cities where subways or trains are connected closely to each other, one stop in Kurume could be quite far apart and getting to places for-example, Narita San, would be better off via Bus as there are no stations nearby that area. I however found taking the trains a better option if you are heading out of town ie. to Dazaifu or Kumamoto etc. But honestly I do enjoy bus journeys, espeially if I get a window seat so I can see the view!