The sound of water, the fresh breezes, etc. is all very relaxing. But I would think that for the majority of people, they are near the shore while on vacation - so relaxing anyway, whether it was at the beach or a golf course in Arizona.
I find freshwater to be more relaxing. I always hate having to shuffle my feet to avoid stepping on a sting ray, or feeling seaweed and thinking it was a jelly fish. Was never too worried about sharks.
A lake getaway is great too.