If you already know what is wrong and just need a doctor’s note (and maybe antibiotics), go to the clinic.

If something is bothering you, but you can tolerate it for a couple weeks, schedule an appointment with primary care.

If you don’t know what’s wrong, or you need something more than a note and a prescription, and you can transport yourself, go to urgent care.

The only time you should go to the ER voluntarily is if urgent care sends you there. Any other trip to the ER should be because someone dragged you there without giving you a choice.