I'd flown a few times with a padded ski bag with no wheels a few times in the 1990s. When I started flying to ski out west with my daughter annually, I got a Sportube 2. When I fly solo, I usually only take one pair of skis. That means there is space for bulky items like snow boots, a backpack, extra gloves, etc. Side benefit is that if I buy a pair of skis during a trip, I can get them home with shipping a pair of skis. That doesn't happen often though.
I have a clamshell-style suitcase bootbag, with wheels. Now that my boots are well used, I keep them with me as carry-on to start a trip but often check that bag on the way home. Then I have a lighter rolling suitcase to deal with during the inevitable layover flying east on Southwest.
What I like for a bootbag is a Transpack Sidekick. Without boots and helmet, it's the same as a regular backpack. I can fit it and the helmet (unattached) under a middle or window seat.
Between the boot suitcase and my Transpack, at the start of the trip I have everything I need for a day or two of skiing. Just in case my checked luggage gets delayed. Hasn't happened to me (knock on wood), but has happened to a ski buddy. Luckily for him, his ski bag made it even though his suitcase didn't. He had enough skiwear and his boots so it didn't make that much difference. He only bought an extra shirt when we stopped by a consignment ski shop.
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Rolling boot suitcase and blue suitcase connected to move around
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