Chloroquine is actually an anti malaria drug. But its anti parasite in design.
Here is a web page on reef 2 reef, tons of reading on different treatments, how they work, what they are, etc.
Lots of great reading there. Most wrasse if not all, and hippo tangs do not do well with Chloroquine phosphate. Hence the need for copper. Copper is toxic to fish, so basically you are killing the parasite and you are slowly killing the fish. However, the fish can last longer than the parasite, so copper works. I dont really like using copper, as you have to really watch the copper levels, test at least twice a day to make sure the levels dont go toxic. Chloroquine is dose once and done. You just would need to add chloroquine back to any water when you do a water change. Ive noticed when dosing copper, you fight appetite suppression initially, and can be hard on the fish. Make sure the fish is eating really good before dosing copper. Using chloroquine, I havent noticed any appetite problems at all.
As SynDen said, copper is hard on the fish. But there are different types of copper treatments. Coppersafe is probably the easiest on the fish, followed by Cupramine.
Using the medicated foods is hit and miss imo. I think you'd need to feed quite a bit of it, for a long time to see permanent and complete results. Ive used Dr. G's, and some fish will not eat it. Soak it in whatever you can, but still some fish wont touch it. Plus you dont want it getting on any corals.