What better, damage over time or imbuement potency on items???
The general multipliers are vuln, dot, and all/poison. On gear, you should be trying to get vuln on amulet, rings, and dot on weapons. If you are asking about masterworking, then probably dot as its additive and will multiply with vuln, and poison multiple on gear. Potency is probably not recommended if you are going pure poison. Also, you should be looking for attack speed as its increases the base damage of dok.
I’mbuement potency is a multiplier. It is a lot more damage than just damage over time (which is additive) when it comes to the masterwork. I originally had damage over time and switched to potency and my damage went up about 30 percent.