Citrate is the least costly generally, widely available, and is the mostly easily taken up in the gut. However, that last quality also helps it to promote high motility in the gut....meaning if you overdo it, you'll be reacquainting yourself with your toilet several times more than usual. Again, 200 mg daily should not put you over the top (healthy kidneys are meant to dispose of excesses of all elements anyway).
There is some, not huge, not particularly strong or compelling, evidence that the other salt formulae are more suited for other requirements. I have not studied them in great detail and don't feel particularly knowledgeable about them. I have personally taken the citrate (doing that for the second time in three years), malate, and bis-glycinate formulae. None of them appeared to affect me unduly, and I can't say they did my any good. I take them mostly just 'cuz. Well, that and I do have atrial fibrillation and want to be sure I'm not working against the successful ablation I had two years ago. So, I take it as a prophylaxis.

Potassium: Be careful on taking potassium supplements. I had read posts on MCC about how well potassium works with PVCs. I checked my EP. He came back with your recent blood test showing you are at the high end of normal on potassium. We do not recommend taking a supplement. I would suggest having a blood test if going to take a potassium supplement.

Magnesium: My EP did recommend me taking magnesium for PVCs. He recommended 400 mg. I came back with question of which formula as there were so many.

EP said he recommends Citrate formula as it is highly absorbable. It is also the most recommended for digestive help also based on the absorbability factor too. EP said his second choice would be Glycimate.

My EP is the Director of Pace Clinic and Electrophysiology at Mayo Jacksonville.