There is no 'best' antidepressant - everyone responds differently to the various classes and drugs within the classes. Generally the first line in antidepressants these days are the SSRIs, and they have generally few interactions, although you won't be able to use MDMA while you are on them, and they might interfere with some other drugs like tramadol if that is your thing. There are other classes but these days they are generally tried if SSRIs fail. You probably wouldn't want them either if interactions are a problem, particularly the MAOI class which interacts with everything, including cheese (I'm serious about that). You'll need a prescription for almost any strong antidepressant though.
As far as over the counter, your best option is St John's Wort. It has been clinically proven to be effective in relieving mild to moderate depression, however, it is ineffective in major depression. It also has numerous drug interactions which most people are unaware of; it has SSRI qualities and also acts as an inducer of CYP3A4 so it's important to be wary when taking this...It often proves a headache for patients who take it along with oral contraceptives, unaware that it induces their metabolism, only to wind up unexpectedly pregnant....
