Doug more or less said it right that airbags weigh too much. Airbags are also overly complicated and there's a "luck factor" with airbags in not impacting on a sharp rock. Despite being based upon airbags, I strongly believe that we should send MER clones to Mars because we've already paid for the development cost and MER has shown itself to be a champion. However when starting from a clean piece of paper, airbags are an unattractive design.

It would be nice if a payload could go all the way down on a parachute. However the terminal velocity for a reasonable sized parachute is too high. Surface penetrators are too much of a crap shoot with all the hard igneous rocks on Mars. Landing on liquid fueled variable thrust rockets as used with Viking and Mars Polar Lander are complicated and intrinsicly expensive. Sky crane is just nuts. Quite frankly, I don't know what's the best solution for a cheap and reliable Mars lander. Maybe a parachute coupled with hydrogen filled balloon? Possibly a super wide diameter two stage turbine / helicopter, refer to:

http://www.ebigchina.com/ebcps/4/pd/222096.html

http://www.enotalone.com/toys/images/B0001XQL90.html

I gave my son one of these for his birthday. It's a really cool toy and doesn't cost much ($20). If one remade it out of graphite epoxy composite, scaled it up by a factor five and had many more blades then (maybe?) it could work on Mars.

It's not an easy problem to solve. I'm puzzling over it.

Gary