I fly with the hard Serfas case. If you can't get a loaner from a shop watch craigslist. I see them for sale on there pretty often (usually for about $150). If you care about your bike the hard case is worth it. Its also worth it to pay the extra bucks and let the airlines know its a bike. If anything happens to your bike you are in a lot better shape.

cardboard box with all the extras (Specifically the drop out spacers and the wide plastic ends to go over the ends of your axles) would be 2nd best.

The wheels will fit in the box. The will not fit in any overhead compartment.... especially during crowded holiday travel.