Technically, the main thing that lag affects is reaction speeds. So things that are barely reactable in vMelee become unreactable. Characters who have to techchase a lot get a little more difficult and some of their things are a little worse. Characters with barely reactable recoveries (spacies) become better.

In practice though and with stuff like lag spikes, big hitboxes that do a lot of damage just become 10x more potent. Peach, Samus, ICs, Luigi, Ganondorf, etc. It's hard to be as precise as we are on a CRT on netplay, which makes these big faceroll-y strategies harder to consistently beat.

I dunno how much that holds true through different skill levels, but that's how I feel about it now.

Basically, spacies are harder to punish though it's easier to cheese grabs off of them in a way (whiff punishing Fox is way harder though). Characters with ganondorf hitboxes (Peach, Samus, Luigi, Ganondorf, Doc) are harder to consistently avoid, and Puff feels harder to kill since CRT kill confirms are already pretty frame tight on her. I think Marth gets mollywhopped by Samus on netplay too since he can't react to her landing anymore and loldsmash.