From best to good: Phoenix, Graboid, Lava Golem, Phase Dragon, Forest Spirit, Elite Charger.
Phoenix complemented Fire like no other card could have ever done. Before it, Fire was a glass cannon. After it, it became a lead cannon.
Graboid can be combined with any element to make it rushy. It simply has the best damage-to-quanta ratio with a high attack that makes it very much worth the card space.
Lava Golem starts out strong and never stops getting stronger. Admittedly it's mainly good thanks to Immo, but nonetheless no one can deny its power. Quinted in a domination deck is a winner.
Phase Dragon has the best card space-to-damage ratio in the game. It's the backbone of any invulnerable army, whether you're facing Pandebonium or don't want to get CC'd as you avoid everything with Dim Shield.
Forest Spirit is used in virtually all speedbows, and I love it for its cheap cost, fast gain and usefulness.
Now that we can change our votes, I change from Forest Spirit to Elite Charger. Yes, Sapphire Charger is weak, but I use Fracharge too much to deny Charger a spot on the top 5. It's so unstoppable. <3