Tried most of them... even
Redscape, but Dip seems to have died there.
webDip: OK. Lower quality map. Unusual support order configuration as in "support to... from..." rather than the conventional "from... to..." and that threw me. Forum is OK now it's php based but still a number of people who hold anti-Playdip grudges which is a little sad.
vDip: Don't think I've ever played there but I've been there. Forum is still atrocious. Probably the place if you want to try automated variants but be aware that errors in coding aren't always addressed, unfortunately.
Backstabbr: OK. Good Sandbox feature which is, perhaps, easier to use than Playdip's Orders Solver but it's more what you're used to, I think. No forum. One aspect of play there that totally threw me but I honestly can't remember what it was and I'm not going to mess another game up finding out what it is again!
Various Apps - Diplicity, Conspiracy: Low quality play, in my experience. Deadlines either severely limited or always too short for slow-paced me. Not tried Primacy yet... not tempted to, frankly. Apps... pfft.
Diplomaticcorp: Dipped my toe in. Not for me.
Playdip: Woohoo. 'Nuff said. Payments readily received to my Paypal account

Community-wise certainly the best, IMHO. Usually the best maps (although WitA is a little unclear in places). Just needs to get a little more Mod and development support going again, I think. super_dipsy is carrying too much.