I've enjoyed Rollins as a heel. I think he's done a pretty great job in that character and held his own on the mic. Certainly some guilt by association as far as being dragged down by some poor storylines involving HHH/Steph, but he hasn't devolved into the self-parody that their recent promos have become. His in-ring is probably a better fit as a babyface, but he's integrating J&J, Show and other shortcuts pretty well at this point. If the goal is headlining with the title heel, I don't think he's at all there yet as the presentation is still too dependent on these other characters.
At this point I think they've done more to solidly establish him as a singles act than either Reigns or Ambrose. I know, you can argue that's a backhanded compliment and not a high standard, but its definitely a statement I didn't expect to be making heading into Mania.