In my opinion the DD subs are a better buy, but with either the DD or the strokers you are sacrificing alot of sound quality.
If you want a sub that has alot of clean stroke(Xmax) take a look at the Audio Mobile MASS 12's, its a clean sub with 600 watts rms power handling and 20mm of one way excursion( the infinity perfect 12 has 14.5mm, JL audio 12w6 has 12.5mm and the kicker L7 has 12.5mm, for example)
I like subs with alot of excursion and my personal favorites are the eclipse 8700 and 8800's, crystal cmp and the audio mobile mass 12, all these subs have a minimum of 18mm of Xmax and lightning fast response to make up for their huge cone travel. The end result is, you get a sub that goes really, really loud and sounds good doing it too.
Its all fun and games untill someone breaks an eardrum-stones