It would depend on what you plan on treating with it I suppose. Personally, the only medication I use is Prazipro to treat all new fish in QT. To avoid using anything else, new additions go through the tank transfer method to rid them of parasites. If I had to, Chloroquine phosphate would be my first choice as a stronger medication
Remember that formalin is toxic - IMHO it should be avoided if at all possible, and you can't make me use anything with copper in it for the same reason.