I definitely feel like the quality here is superior to the other sites I've been at. Specifically, I had very brief tenures at PlayDiplomacy and the Facebook app. PlayDiplomacy games generally seemed to have less communicable players with inferior tactics all-around; even in the fledgling stages of my career I found myself playing very well for the positions I'd find myself in. I say "for the positions I'd find myself in" because my actual tenure there was not very successful: every game I played had a crucial CD or several CDes early. When I couldn't get any pauses on the games I was in while I went to a national debate tournament in late May, I just never came back. I stayed here (I had just started out here at the time) and I'm glad I did.
And Facebook Diplomacy is just horrendous. I'm in a high-stakes game that supposedly has several top-100 players or so and they'd be middle of the road here, no question. Granted, I've seen a couple of very good players there, and I'm sure the top tier there could handle the upper echelon here, but the quality of play outside of that group is not very good. And CDes are a huge problem. Thanks to both, I'm about to win as Italy... in 1906... with 11 units. I KOed Austria by about 1903, Turkey CDed, Russia got in trouble up north and the West ignored me completely (plus France is about to CD...). I just feel like this wouldn't happen in comparably-important games here.
Also played on vdiplomacy, but seeing as how it's basically the same community on a variant-themed version of this site, I don't think there's much to say.
Maybe I have a colored opinion; I'm no veteran of any of those other sites. But I feel like this site has the best quality of play of anywhere I've tried.
For those that are veterans of other auto-adjudicator sites, e-mail, zine or f2f circles, what do you think of these thoughts and more importantly how do you think webDiplomacy stacks up with the other Diplomacy venues?