THe aluminum versus steel versus tintanium versus unobtainium is a debate that has been around for years.

And for the aspect of "harshness" I believe it to be baloney because the comparisons are never equal. Changes in tire, rim, spoke count, saddle, frame size, fit, and surface ridden all contribute. Then again, why believe me?

Read what smarter people have to say:

http://www.sheldonbrown.com/rinard_frametest.html