A pat on the head is better than some kind words to your dog, found a study from January. If they have a choice, dogs will always take petting over praise, and that was found among shelter dogs and those with owners.

Phrased in fancy science talk: "We first assessed preference using a concurrent choice procedure in which dogs were able to choose between interacting with a person providing petting or a person providing vocal praise. The time allocated to available alternatives can be used as a measure of preference (Baum and Rachlin, 1969), in this case dogs’ preference for different types of human social interaction. By measuring proximity, our results might point to interactions that could be relevant in producing attachment behaviors."

But the more relevant take-home message I saw via Emily Anthes on Twitter:
Citation: Erica N. Feuerbachera, Clive D.L. Wynne, Shut up and pet me! Domestic dogs (Canis lupus familiaris) prefer petting to vocal praise in concurrent and single-alternative choice procedures, Behavioural Processes Volume 110, January 2015, Pages 47–59 doi:10.1016/j.beproc.2014.08.019