I travel very often with my concert (classical) guitar for concerts and I often found myself in low cost companies which only accepted the guitar on board if its in a soft case. Otherwise I had to either give it or pay for another seat, depending on the company's policy.
I came up with this BAM case, which is already a very good brand, and I must say that it didn't let me down with this product. It is very resistant, light, water proof and with lots of pockets (which comes in very handy when traveling). I can finally travel with a more peaceful mind knowing that the hard foam inside this case will protect my expensive instrument from the minor handling hits of going around with the guitar. Obviously, one should never give the guitar to be checked-in in the plane with such case, it won't survive the trip. But if its with you all the time, its perfect for it.
For me it has been a great addition to my equipment and saved me lots of money with double plane tickets!