I went for Quix because of price point and he is really good.
Then I upgraded these cards to silver level : Naga Brute - gets Thorns, Naga Assassin - gets Backfire, Manticore - Reach (I got only lvl 1 because of price), Djinn Chwala - Thorns, Chaos Dragon - gets Blast, Dessert Dragon - gets piercing and Void dragon. These are very strong cards even if you can not afford to upgrade them much. After this the Dragon cards starts getting very expensive. The Vigilator is on my list. Double hit with range and melee - in opportunity, or Melee Mayhem etc, he is insane. Dragon Jumper is awesome as well but they start to cost quite a bit. In tournaments having a couple of these cards will make you stand out.
Good luck