Well being a wheelchair user, I can immediately eliminate two of those options. I can’t ride a bike, and the logistics of travelling by bus would be impractical and far too time consuming for me.
That leaves airplane, train or car. Airplanes require a LOT of organising, and worry over the chair being in one piece at the other end, so wouldn’t be my choice just for a trip across country, though I have taken my powerchair abroad.
I love train travel, and would probably choose this as you can relax and enjoy the scenery, and get a drink or snack easily, and most importantly you don’t have to break up the drive to hunt for a toilet as there will be one on the train, and at most train stations as well.
If I was intending to stay over somewhere for a few days (or more), I’d probably abandon the train idea purely for the practical reason that I’d have more luggage, and this would be easier to travel with by car, and not need lugging around on the journey there and back.
The other thing that would dictate whether it was car or train, would be the transport network availability at my longed for destination, if it was in/near a big town or city the train would be more likely, but if it was somewhere rural then the car would make more practical sense for me personally.