Yeah balloons are awesome at level 3+ but I've managed to work out if you can lure it with something like cannon, then use a muskateer, they're easy pickingsBalloons absolutely wreck my current deck. I only have Spear Goblins, plus Fireball and/or Zap to counter it. Luckily it doesn't pop up to often.
You can expand that to any air heavy deck I guess, but Minion/Horde is easily taken care of.