I think I prefer the first one (Ice! skate! profiles! half-open mouth! YAY), but each has its merits... The fourth one is great to write a title in and is hot (although the heads & chest don't really fit my idea of John & Rodney, and the pants of the skating guy arent't tight enough!), the third is just peaceful and warm (with a hint of hotness in the lacings!), and I like the skating guy on the second one but the position of the arms of the guy in green are justt a bit off to me...
You can still use all of them all through the fic, of course ;-)
And, finally, my opinion isn't worth much since I'm waiting for this fic to be finished before reading it, so... I only know it'sn ice-skating AU so far ;-)