Venture co is almost a surefire way to lose against a paladin if you don't bait a bunch of shit first, Aldor peacekeeper or humility on it screws you completely since you now have a really shitty minion that prevents you from playing the rest of your shit. Mages can also be bad if you play it too early, if it stays frozen for 2-3turns and eventually gets pinged, it's a huge waste(granted playing more shit probably wouldn't have helped since they'd be frozen too but who knows). Against other classes though I tend to play it turn 5 regardless of what else I have(unless I absolutely need silence/taunt etc obviously), and force the opponent to deal with it asap.
Also wtf EU battle.net down for over 24h, is this 2004 again?