What it says on the tin.
I'm mostly on Griffonia, even though I have the worst ping there, because most of the people I know are there.
I've been running around Zebrica on day 1. But I'll try to be on Griffonia now. ^-^
EDIT: Having issues connecting to Griffonia for the moment. Will be on Zebrica otherwise.
Lag and ping isn't a problem for me so I'll join you guys on Griffonia! :D
I always join whichever one has the lowest ping at the time. The downside is that there aren't as many people around, but I want to be able to explore the game as much as I can during the OSWs. I absolutely love it so far. Amazing accomplishment, especially considering that the people working on this are doing it for free, as far as I know.
The only things I saw that I felt could be improved were pretty minor things. I'm pretty sure I first played LoE in 2012, maybe 2013, and the game has come a long way since then.