What cl should I continue to level: Priest or DK?

I have an 80 shaman that is pretty freaking geared. So since that I have made a dk and a priest. both are 70. Now because I already have a healer one would say oooooo make a dk. well EVERYONE is a dk and I'm just not sure about it. I love priests but would having 2 healer cles really be that smart. Anyways, what are your thoughts???