When a ring fits properly, it does not spin. However, some people have larger knuckles and in order to get the ring on, it has to be large enough to make it past the knuckle. Then it is too loose on the lower finger. This really is not the fault of the ring; it is the way the finger is. Of course, your ring might just be too big!
My ering is set on an eternity band, my current ring is the one on the left:
And here's a horrible shot of my wedding set that I just took. I'm really the world's worst photographer, sorry!
The stones in my ering are 4-pointers, the stones in my wedding band are 7-pointers. The rings are size 6 (ering) and 6.5. I really wear a 5.5 but I prefer my rings to be loose, so I upsize.