What is everyone riding?
I can feel a difference in speed and comfort when switching (nearly) identical wheelsets from 28's to 25's and even 23's. I've got 28's on now and happy to keep them there for the yucky months - but am disappointed at the perceived change in effort / speed. I was hoping to ride them next season for events - as they are more comfy for the long haul - but I'm not so sure.
In the last few years I've run:
Bontrager 23's (slicks) - not sure of the model - but they wore quickly.
Continental GP 4 Seasons 23's
Continental GP 4 Season 25's
Bontrager 32's (a touring tire)
Scwalbe Marathon 28's (which I was hoping to make into my brevet tires, but I'm not so sure...)
Of my recent rides I like the Conti 25's the best. Still going strong after a full brevet season (and all the riding in between) - and no real complaints from perceived "slowness" from a tougher tire. They did very well on our local 600k with some sections of ugly gravel and dirt.