I say both, and also 'Thank you very much' or 'You're very kind, thank you.' In my Hubs I may end with Much peace or Loving thoughts, etc. Point here is that our Thanks or thank you's are influenced by our state of consciousness, and who or what is presented to us in the external environment as well as their acts of kindness or insincerity.
This affects us consciously or unconsciously, and we respond in kind.
I prefer 'thank you' and even more than this, but again it can depend on the interaction and states of spirit from both sides at the given moment.' Thank you so much' for asking this question Dora (smile)