There's no one right answer. A gigbag is very definitely easier to haul around; a hard case is very definitely better protection.

I tend to look at the value of the instrument. If I could replace it for $700 or $800 US, a gigbag is probably an acceptable risk if I get a good quality one and I'm careful. If it would cost much more than that to replace it, or it's not replaceable at all, a hard case is certainly indicated.

Of course, if you're going by commercial air, you either get a Calton case, leave it home, or ship it out to meet you.

Peter.