Red-eyes. Because it's cheap but still strong. Try to get the support in Black Rose Dragon box, it has lot of red-eyes support there.
If you buy 3x, it’s a toss-up between Ancient Gears straight up or Fire Kings peppered with the Yubel chain. Then again, one can never go wrong with E. Hero Neos.
You can buy all HEROes structure decks and make a pretty cheap deck around them.
imo its the newest one, on its own its incredibly powerful, you can summon a 2700 atk monster in a multitude of ways, and one of them destroys all monsters on the field, meaning its hard for opponents to deal with.