I would go for salt first, short term (a few weeks, however long to treat) will not harm the pleco. Most of the meds. are so strong, they are much more stressful than salt would be
In general medications will have more negative effect on the fish. The levels of salt needed for the ich treatment are considerably low. Now take that with a grain of salt , being that the information I have has been mostly aquired from this site, mostly through daveedka. Being that he almost always posts a link to scientific data as well as specifics to his own experience, AND admits when he doesnt know the answers, Id be willing to bet my life savings he is spot on with his info.