My personal preference for a Coromandel stopover would be Pauanui over Whitianga - more picturesque and walking distance to beaches/accomodation/dining/bars.
Yep, agreed Pauanui is very nice and an easy walk to the shops etc and well worth a lunch stop. However there is much less choice in accomodation/dining/bars(are there any bars in Pauanui except for the Pauanui Club?). Also there's more to do close to Whitianga, Hot Water beach, Cathedral Cove, kayaking etc. Plus there's fuel at Whitianga.