Tried both and it was a VERY close call...I still prefer the S4.
HOWEVER, if you're going for the turbine pro gold or copper, then it's no challenge to the S4...they just out flat destroy the S4 in pretty much every aspect.
You can get the Gold turbine pro at JandR for $80- than the amazon price. If you have the $ for them, I'd get them immediately.
EDIT: the only thing about the S4 is that they break down after a couple of months of use...the built and life quality of them isn't as impressive. I already had them break down twice...the second time just a few days ago...now I need to find my receipt to receive a new pair from Klipsch.
I bought the turbines from Best Buy, and within a few days the housing started to come unglued. It eventually came off completely, so these are on my "back to the store" list.
Another thing, there's just something about the Turbines that I can see myself becoming bored of within a few weeks. That's another reason they're going back. Even when used in bass heavy genres they should excel in, something about them just didn't do it for me. I haven't listened to the S4s in awhile, but they didn't leave the same impression the Turbines will.