I have a BIKND. I did a LOT of research on these before I bought one and was lucky enough to find it on Wiggle on sale for about $500. Here were my findings:
BIKND:
1. Blow up sides allowing the bag to pack neatly down for storage. When blown up they provide substantial cushioning for the bike;
2. 4 recessed wheels. Easy to wheel around the terminal. Also less likely to be knocked off;
3. 4 wheels can be packed;
4. When we went to the US last year we were able to fit 1 bike and 1 frame in the bag. I doubt you'd get 2 bikes in any bags on the market at the moment;
5. Weighs 11kg. This is on the heavy side. Was fine for international travel but I have been stung domestically.
6. I am short so I don't have to take the seat post off. Most would but that is a bonus for me.
SCICON
1. 4 wheeler but they stick out and I've heard stories of them being knocked off;
2. You don't have to take the handlebars off (or pedals though most people do). Huge advantage for those not familiar with bike assembly;
3. Does not pack down for storage and it's pretty large.
HARD CASE
1. Less flexibility when fitting in additional items such as helmets etc;
2. Does not pack down for storage;
Have a look at
Bike Radar for reviews though this is an old article.