Online. By at least a factor of two. Our recent article entitled Lessons learnt from organizing a virtual conference discusses some of our technology choices and how we leveraged them to put on a successful online meeting. That article touches briefly on some of the challenges we faced, but it doesn't fully convey how much work it was–both in advance and during the event.
A Tue, study studied this question.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: