I love salt lamps. I started with the candle and it had a really good effect on my emotions, stability-wise. So I bought another, a plug-in kind, and put that next to my bed all night and slept like a baby (30 watts, dimmer switch). Then I got a big one for the living room, and that's good too. Salt lamps are sort of an on-going project with me, I gotta save up to get one.
If I had to have just one, I'd get the candle because I can move it around from room to room (even the bathroom with no plugs).
fwiw, I get mine from Solay.
I almost forgot to comment on the science - that's because I don't know - except that the thing about ions always works well on me.