Well, the last design looks very much like a stealth bomber, so I don't quite understand how this design helps a commercial plane.
The first, design seems to be an improvement of the current designs and my guess is that it is safer in case there is a problem with the engine, as if it blows up, the parts are most likely to spread on the sides (due to the conservation of the angular momentum), thus making it safer for the passengers.
Now the second design, I wouldn't say it is not strong or stable, as it was designed by Northrop Grumman after all, not Joe the Plumber! My guess is that would mainly carry cargo.
Personally, I prefer the first (Lockheed Martin) design and I find the second and third not very appealing
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