For my money definitely, absolutely, and totally the best with a long term partner. We know each other, care about each other, have discovered each other's likes and dislikes, and can also laugh about it all - because sex, as well as being very, very pleasant is quite funny too and shouldn't be taken too seriously.
And things like anal sex, which we do every once in a while, need so much in the way of relaxation, communication and unhurried, unpressured preparation for it to be really, really good, could never be the same on a one night stand. I couldn't imagine it to be anyway.
Sex, which for me has been exclusively with the same woman for over twenty five years has only got better. And that's not because it's all been plain sailing because it most definitely hasn't been and there have been some real ups and downs sometimes and the need for give and take at times.
But I can honestly say that it's now the best it's ever been - better even than the heady early days. Especially over the last few years when we've found we've sort of "matured" into each other, if that makes sense.