I'm mercury toxic and I've been reading chelation protocols now for over 6 months.
From what I've read so far, hands down, DMSA is the best way to go. 100 mg per day, start slow.
I'll be taking 12.5 mg every 4 hours, day and night, for 3 days, 11 days off.
Many of the natural chelators don't bind with heavy metals strongly enough, they don't claw them out of the tissues strongly enough, and end up redistributing. I think they are good for "the regular person" or someone with minor problems, but not for people with heavy toxicity.
At low levels, DMSA has also been proven safe, has been around since the 1950s, and has been used to chelate lead from children. And in my reading has been used successfully by people recovering from MS and other serious diseases. It's a tried and proven way from what I've read.