Tokyo - Sapporo winter, transport?

Hi there,
I am planning on my visit to Sapporo in mid-late winter 2019 and trying to figure which transport would be most reliable up there.

I have travelled by train as well as flight there but that was during summer months.

I expect it to be quite a lot of snow so I was thinking of possible delays / cancellations.

So, what would be the most reliable way?

It's one of the busiest flight paths in the world, just fly. The train takes so long, even if the flight is delayed it probably won't be THAT long.

Thank you for your reply. I only herad Tokyo - Fukuoka is the busiest line, did not know Tokyo - Sappor was that busy as well.

I think I read something about severe snowstorms affecting transport around Sapporo this or last year. Since Sapporo will be my last visit before returning to home a few days later I dont want to be stuck up there.