I've used both hard and soft-shelled cases. There is no right answer. Here's my take on this.
- Used to have a Pedal Pack and a SciCon. The Pedal Pack was bombproof. Superb latches. Easy to open close. Much like a big suitcase. Not only is the outer shwell hard, there is ample foam padding inside. The big downside is that it is HEAVY! It is really easy to go over the weight limit with airlines shrinking weight restrictions and they charge you alot when you do go over. The SciCon hardshell really sucked in comparison. IMO, it's way overpriced. Unless you live in Italy and can get a deal, I wouldn't bother. The latches are not as good and there is very little padding compared to the Pedal Pack. In fact, I got back from an overseas flight once and one of the latches on the SciCon case was damaged. I had to bend it back with some pliers, but after that it never worked well. If you only want major protection for your bike and don't pack alot of other things in your bike case (like clothes, shoes, etc), then the Pedal Pack is the best. However, as soon as you pack even a few shirts and shorts in their, the weight really adds up and puts you most times over most airlines weight limit. Also problematic is that I am not sure if Pedal Pack is even in business anymore. It would be cost-prohibitive for most people outside of the USA also as it is an American case company.
I have used two. One of them (can't remember the name) where there was a bottom steel rail system to hold the frame and wheels. Worked pretty good. The big advantage is much lower weight compared to some heavy-duty hard cases, so you can stuff some more stuff in there. My latest case is the Pika case. It's a soft-shelled case made in the US. A bit expensive for a soft case. Truthfully, I am a bit underwhelmed. It does have good padding, and better than my old soft shelled case, but for the price it isn't much better than the other soft-shelled cheap case I had. I also found that even though the Pika is pretty tight, it you don't pack the frame in their just perfectly, then the frame will move inside the case slightly. This happened to me and I got a nice scratch right over the down tube and seat tube. more my fault, but still not happy about that. The other soft case had the rail system at the bottom that seemed to hold the frame more rigidly inside the soft case. If I had to do it again and get a soft-shelled case, I would get the cheap one with the bottom metal rail system, and buy extra pipe insulation at eh hardware store for extra protection.
In summary, there is no one best case. Baggage handlers will screw up anything. Hard or soft.