There are better plants than others, do you mean medical? A. Thaliana is a good plant for it, however it would be difficult to make a judgement, (not necessarily terrible, but I do think there are better than others). I supose I have to include there are better than others. Plants that grow on acid soil are an "example".The amount are small, you could still try for plant biotechnology (phytomining)

Thank you Talal A. Zari

What metal compounds are you researching?

Mercury, lead, and Cadmium Alexandr Voronin

Sample preparation for mercury requires special attention. Losses of mercury up to 90% are possible.