I personally found DMPS to be much stronger and more effective than DMSA. The combination of DMPS and RLA cleaned up my brain to the point where I don't really perceive a difference between my brain function now and before I got sick. I never thought I'd say that, as nuts as I felt three years ago.
I bought DMPS online as the brand name Mercout. It was expensive but well worth the price. I actually bought two bottles about a year apart.