I experience motion sickness more easily on planes than on trains or buses. Boats are a problem too, in heavy seas.
In a large plane with no or very light turbulence the motion sickness doesn't brake through, it's only an uneasy feeling. In heavier turbulence, or in things like a small Cessna or a sailplane it gets worse. I haven't had to vomit in these situations since I was a little kid, but I do feel bad from nausea.
From my experience bus was the worst as you can't get front seat, even worse were backward positioned seats. Train and plane were great. Car in the middle, depend on road and driving style.
If I was on bus during childhood you would know by stops it made. We avoided that by traveling by car.
There's a non-drowsy anti-sickness formula out now called meclizine, but I found it to be less effective.