TeenHealthFX understands your asking which works better, but we do not endorse any commercial products. We are also skeptical of products whose claims sound too good to be true. We have no knowledge if ZenMed works as they claim or not. However, since you say it is cheaper than going to a skin clinic, you may want to give it try first and see if it improves your acne before going to your skin clinic.
You say you have tried several medications and that none worked. TeenHealthFX recommends that you talk to your doctor about other treatment options that could be beneficial, including phototherapy. Your doctor can tell you about the drawbacks and benefits of each.
Check out our answers to other questions teens had about acne: Acne Problem and What Do I Do About Acne? for more information about acne and its treatment and how you can take care of your skin.