I used to travel with two cases, a Fellini for my Joss and a good 1x1 box case for my break cue. I flew a lot internationally with those two just packed in a military duffle bag with all my clothes and stuff packed around them.
But, every time this comes up I will say the "best" is an ATA case. It certainly may not be the right choice for many players and occasions.
I remember a person traveling with a real Stradivarius violin. They actually bought a seat on the plane for the violin. That wasn't always allowed, so sometimes it had to go in the cargo/luggage hold. The case alone was worth more than most violins, so the case had a case. They either paid for an extra seat, or they paid extra for the luggage because of the size/weight of that specially made ATA case. Their violin bows were another story altogether and the case and bows were probably more valuable than most houses.
Personally, I have gotten back to case making. I have been thinking to address the matter of a specialty case for flights. And I mean for individual cues, like a 1x2 or something like that, not the big dealer/collector ATA cases. It could potentially also be for shipping valuable cues. I have my ideas, we will see if I do anything with them.