Mercurius
Legend
Both/neither. I tend to have a "session 0.5": Half making characters, setting the stage for the setting, and the other half beginning the campaign.
All of the times I've DMed over the last 10+ years have been bi-weekly, with semi-frequent cancellations due to busy lives, so a session zero isn't practical. I try to do some of the session zero work via email: Send a setting and character primer, ask people to think about what they want to play, etc. Then roughly half of the first session has been making characters and verbally summarizing stuff from the primer, and half the beginnings of an adventure - set-up, a bit of role-play, and one combat.
All of the times I've DMed over the last 10+ years have been bi-weekly, with semi-frequent cancellations due to busy lives, so a session zero isn't practical. I try to do some of the session zero work via email: Send a setting and character primer, ask people to think about what they want to play, etc. Then roughly half of the first session has been making characters and verbally summarizing stuff from the primer, and half the beginnings of an adventure - set-up, a bit of role-play, and one combat.