I realised recently that my shorts have a netting like swimming shorts do and decided to ditch the boxers and see how it was. What an absolute game changer! I don't know why I didn't do this a year ago when I started running.
Always underwear. Aside from the netting being coarse on my delicate skin down there other people don't want to see my cock swinging around so blatantly in my shorts. I've seen it on other people and it isn't a good look. Also swinging free like that is super uncomfortable for me, I want my shit locked down and not slamming into my legs!