Same frame and materials used across the Defy range. So no difference in comfort or ride quality, only difference is stopping in the wet. Wasn't suggesting you get the disc model, more a comment on the frameset. Not sure 28s n guards are possible, I used sks raceguards xl, clip on jobs.
I have the Defy disc 1, not ridden either of the other two, can recommend it for all day comfort, you can also get 28mm tyres in it.