I definitely find it takes both to make a good scene.
I've found that the best combination for me is starting with the psychological, I'm a sucker for words in general, a few growled sentences and I can be totally gone. But in order for me to really his subspace and stay there I need that to be followed up with the physical.
Best scene I ever had started with a two hour drive in which he just talked to me, then followed by a harsh spanking. I had melted completely by the time we stopped driving and didn't really come out of it until the next day.
If I had to pick I'd choose psychological, but I really can't imagine them actually being completely separate entities. They blend into each other and overlap.
And as usual there have been many people saying similar things but far more articulately already in this thread, so I'll just say a general, 'Yeah, what they said!'