No comment about the "UFO" shape! 
Awwwww... That's the best one
Again, very interesting links. (You learn stuff on this forum!)
Again, you're welcome! (And I used to think you couldn't learn anything on the internet
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So I should have said: "the only serious proposal to use rotors all the way through the atmosphere to landing that I know of is Roton."
Probably, but it would be simply petty to bring that up
The use of rotors is very attractive but the engineering challenges to using them to land a spacecraft seem formidable. Do you have the rotors extended in some way through the whole re-entry like Roton, or do you deploy them at low Mach numbers just before landing?
I've only glanced at the stuff you linked. Have studies been made where the rotors are exposed to re-entry heating? If you wish to avoid that and deploy the blades just before landing, how mechanically complicated would that be? And how safe would that be compared with ordinary parachutes?
Again it "depends" on the various assumptions on the design. In the majority of designs that assumed rotor use with blunt-body reentry it seems the "deploy-before-entry" method was prefered but the more recent concepts tend to favor deployable rotors at subsonic speeds. (Yes various materials were studied for the rotors and various methods for TPS and cooling during entry)
Roto-Chute was (as far as I can tell) simply going to use high-temperature materials, while ROTON was going to use active cooling (water) both for the heat shield and the rotors. ("Active" TPS tends to be less often proposed because of the feeling since it's "active" any failure or low performance would lead to disaster. As it's "active" rather than "passive" chances OF failure as assumed to be higher. But since "passive" systems tend to be "beefed-up" in order to avoid failure the difference is not as great as many assume)
As to comparing with a parachute, that seems to be the major reason that "other" methods tend to not gain traction. Parachutes (and wings) are KNOWN quantity and are both available and have well documented data to point to. Other methods, not so much.
Just about any landing method requires SOME type of "deployment" segment with some being less "critical" than others in a general way. (Sure, failure to deploy the landing gear on a winged vehicle probably means a serious situation but failure to deploy parachutes, rotors, whatever on a ballistic lander and the situation is pretty terminal)
In most cases it seems that suggested alternate methods of landing (rotor/powered/etc) vertically seem to include "parachutes" as a back up which begs the question if you're going to have them why not simply use them as the primary?
For one thing more than one system gives you failure tolerent "depth" where you can "afford" to lose a system and still recover more or less intact. Even "standard" parachute systems often use this strategy relying on more 'chutes than required in case of a failure.
There is also the issue of controlabilty and guidance where a suggested system allows more accuracy than "normal" parachutes.
In the end it really comes down to the subject of this thread in weighing the "advantages" and "disadvantages" of various factors between systems and between what is desired for the outcome.
Like all things, the answer does tend to come down to simply "It depends" with the solution being highly dependent on what assumptions are being used, what results are desired, and what factors are being considered.
I've seen it "said" over and over again that "wings" (lifting) landing enhance reusablity because you don't have to re-pack the parachutes, But that is such a simplistic comparision as to be useless, and pretty much just highlights an assumed bias.
We have decades of experiance inspecting, packing, and using parachutes so the process' themselves are well known, highly understood, and (probably most important) with well documented and known data readily available. Mounting a fully certified "new" parachute in place of a used one would be a relativly straight-forward task and easily intergrated with the rest of the required vehicle refurbishment in getting ready to re-launch.
"Aerodynamic vehicles have greater cross-range" is another one which tends to disguise a bias rather than a real "factor" since in general the one who quotes this is refering to a winged vehicle veresus a ballistic capsule, but which ignores several dozen questions relating to "aerodynamics" and "cross-range"
Spacecraft are generally designed with SOME "aerodynamic-lift" if for no other reason than to reduce the G-stress' of reentry. However "cross-range" wise the Spacecruiser:
http://www.up-ship.com/apr/extras/scruiser1.htm"spaceplane" had a higher "cross-range" than the Shuttle and it didn't have wings. It would be able to perform manuevers in the upper atmosphere and propulsively return to orbit which the Shuttle can't do. (And as the X-37 is suggested to do but that's another "thing"
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What it could NOT do is "fly" aerodynamically at low-supersonic/subsonic speeds. For that it needed a "parachute" (parafoil actually) and also to land. With a high hypersonic "L/D" it could perform manuvers at much greater velocities where "energy-wise" you get more bang-for-your-buck than supersonic or subsonic. But you "pay" for that at the lower speed ranges, hence the need for parachutes to land with.
But again, that's part of the "needs" driving the design; the Space Shuttel was designed around the "needs" of low-speed handling and landing requirements while the Spacecruiser was designed with other criteria in mind.
"Wings give you more surface area so are easier to design for Low-G/Low-Stress reentry and landing" is another one where you can USE any system to get the result. Soyuz/Apollo/Gemini/etc all used "lift" during reentry to effect g-loads and reentry heat levels the same way the Shuttle did. Again that's a "design" factor not inherent to any one type of vehicle.
We've KNOWN about ballistic coefficent ratio for those factors even before we launched the fist spacecraft, but actually applying it as a design factor has been limited at best.
REALLY want to ensure your payload has the most gentle ride possible? Fine, use a "Para-Shield":
http://microsat.sm.bmstu.ru/e-library/etc/bremsat2.pdfhttp://spacecraft.ssl.umd.edu/publications/2010/SpaceOps2010ParaShieldx.pdfhttp://www.nianet.org/rascal/forum2006/presentations/1010_umd_paper.pdfhttp://www.planetaryprobe.org/SessionFiles/Session4/Papers/Rohrschneider_Inflat&Deploy-Paper.pdfBut it's not really compatable with an aerodynamic landing, so anyone looking for an excuse to use wings or aerodynamic lift is going to gloss right over that...
"Capsules aren't reusable" which is right out there, because again it's design factors. We haven't needed or wanted a "reusable" capsule yet so none have been built. Technically there is not reason a capsule can't be just as "reusable" as a winged or lifting body vehicle.
And those are just a few (very few) of the various "factors" that need to be considered and/or designed to. And pretty much why the ONLY answer in total honesty to the OP question ends up being "It Depends" and why the debate will continue for a LONG, long time to come
Randy
