I use the 2nd tire from the top,( kenda 838), the reason being that thin groove
in the center closes under roller pressure making uniform pressure across the
roller. With a flat slick the most contact pressure is at either side of the center.
The result is better contact and reduced wear. Use this one if you ride mostly
asphalt or concrete or, as Slack said, the top kenda kross if you ride mostly trail
or unimproved road.