Should I rent a car for a Japan ski trip, or stick to trains and buses?

It depends on whether you're building a trip around one resort or several, more than on your confidence behind a wheel. Staying put at a single resort like Niseko or Hakuba, the train and shuttle network covers what you need, and a car mostly just adds parking to think about. The moment your plan involves moving between two or more resorts in a week, driving stops being optional in any practical sense.

Public transport in Japan is patchy almost everywhere it exists, and the timings are usually built around Shinkansen connections and getting guests to residential areas, not around first and last lift. Hakuba, Kitakami and Asahikawa are the exceptions, with genuinely workable bus links. Geto Kogen is reachable this way from Kitakami station. Outside places like that, a vehicle turns a fixed, someone-else's-timetable itinerary into something you can adjust morning to morning, chasing whichever resort actually got the snow overnight.

The genuine downside isn't the roads, which are cleared quickly and well signposted, it's sudden weather. Visibility can drop to almost nothing in a snowstorm with very little warning, which is a different problem to manage than icy roads at home, however experienced you are. Anyone nervous about it is better off easing in on a short local trip before committing to something longer.

On the practical side: hold a booking with free cancellation as soon as you have a rough window, since hire companies open their calendars on very different schedules and the AWD options vanish first. A people-carrier fits four adults and their gear more comfortably than most expect, and it beats paying for four separate train tickets, especially with ski bags to manage getting on and off a busy platform.

If you're staying at one resort and don't want to think about parking, the trains will serve you fine. The car only pays for itself once your plan moves beyond one resort to a multi-resort area.