Clearly for bike protection a hard case is best. A cardboard box generally does OK too and either woudl be a good option if you are using a shipping service. For me though, when I am taking my bike on a plane, handling is a big issue and personally I have decided to sacrifice a bit of protection in the name of handling.

Thats why I use this soft case http://www.groundeffect.co.nz/produc...il-BOD-BAG.htm. At a pinch I can walk short distances with this and a travel back pack. You only need to take off the front wheel and the pedals to get a bike in here.

I've taken it to Australia twice with no ill effects to the bike. BFs frame got a bit of a cosmetic (not structural) ding on our first trip but I don't know if that was from the plane, or from the cattle trucks the bikes were loaded on (not in the bags) to get to the start of the ride.

The first time we went we were waiting by the oversized luggage area, only to see our bikes coming off the normal luggage thing first.