Hey Mox: Well I have ridden all three, currently use conti contacts w/ safety system and Schwalbe Marathons. I have also used the Spec Nimbus Armadillos.
Conti: Most comfortable, 2 flats ~ 2,000 miles
Schwalbe: Comfortable, 1 flat ~ 2,000 miles
Specialized: Harsh 1 flat ~ over 5,000 miles, even rode about 25 miles w/out a chunk of tread that fell off. If you want to try out the front tire(still lots of tread) you are welcome to it. Let me know and I'll bring it down to work. I work in Beltsville, a stones throw from UMCP.

Ride improves with less flat potential. I did not ride the SM Plus. I hear they are very similar to Spec 'dillos. I've even seen Spec 'dillos in 27".
FWIW: 1 or 2 flats in 2,000 miles with a comfortable ride (though slow ride) is good enough for me. The SM(not plus) were the cheapest. 'dillos were the fastest(by far)
Charlie