The knowledge and initial introductions in online events can lead to hugely positive outcomes in the future, so in terms of ROI I think online events are probably far superior, but when I think to my top 100 memorable experiences I've had at events, not a single one of them took place online. Sure, I've met plenty of people that I later became friends/collaborators with in person, but all the memorable stuff happens later in person.

Just a few recent off the top of my head:

- Paddleboard breakouts at East Meets West

- Asking Vinod a question about next-gen registers at Program Synthesis Conference

- Animated discussion about cpu design over beers post conference in SF

- Talking to a startup about IOT management on the roof of an Accel event

And some ones from 10+ years ago:

- When I was a college student sitting on a folding chair and chatting with a nice woman about the startups pitching at TechCrunch40 (turned out to be M Mayer)

- Drew pitching me on Dropbox before launch in Cambridge (boring, I thought)

- Nate pitching me AirBedAndBreakfast in Mountain View (loved the idea from the get go)

The only things that have come close to being memorable online were some recent Teamflow ice breaker type events we did at Our World in Data around the virtual campfire.