So I recently discovered that the supercade client is awesome.
http://damdai.com/supercade/No input delay. I've never seen it desyncs. Fairly smooth though there is some frame rate hiccups from time to time if you don't have a good net (mine sucks). But it's probably the most playable netcade I've seen for emulators like this.
Games we could play:
Co-Op
Alien Vs Predator: Classic beat em up from Capcom's glory days. Each character plays different and has a wide variety of moves.
Mars Matrix: Addictive vertically scrolling shmup that lets you deflect bullets with a recharging shield.
Metal Slug: Run and gun 2d action platformer. Very hard and very fun.
Vs
Samurai Showdown: Classic weapon based 2d fighting game
Twinkle Star Sprites: Vs shmup where killing enemies sends them to your opponents screen.
And pretty much every fighting game.