I'm happy with a soft bag. I've used one for 10 years - and a padded one for only 5. My skis have never had a scratch. As with all baggage, the airline will put miles on it, though.
This year I plan on traveling with 2 skis. I'm wondering if I need a wheeled bag. Two pair of skis, along with all the other bulky gear, is a lot to move from car to airport. Although I usually get a ride or take a taxi. So.. I don't know.
ETA: The problem I would have with sporttube, I think, is that when I fly, I usually go in groups. Fitting 4 or 5 people + gear into an SUV is hard enough without a giant box of air to fit in as well. I already think I'm going to get cross looks traveling with 2 skis