Can't quite decide.
I plan on shooting suppressed most of the time.
http://www.ruger.com/micros/rpr/models.html
.308
+More common ammo
+Shorter barrel (20" vs 24")
+More subsonic ammo available
6.5 Creedmoor
+More accurate
+Less recoil
+Match ammo is actually cheaper than .308
Thoughts...