Verified answer

Dragonite is highly versitile, learning almost any type move you need him too, though he has a x4 weakness to ice.

Volcarona is one of the best bug types there is. He is also very good at learning other type moves.

Seeing your team though, I'd go with

Volarona ( good against bug, dark, psychic, grass, steel)

Zekrom (everyteam should have a dragon and an electric type)

and probably Lucario (fighting is great for offense, steel is good for defense)

Dragonite is a great choice if another isn't working out.

Volcarona is a great special sweeper, especially when at level 100 - when it learns Fiery Dance. A moveset of Fiery Dance, Quiver Dance, Bug Buzz and Hidden Power Rock, Ground or Psychic uses Volcarona's awesome stats in speed, special defense and special attack, as Quiver Dance boosts them.

Reshiram is awesome - A moveset of Flame Charge, Fusion Flare, Blue Flare and Dragon Pulse is good; it raises Reshiram's speed. Alternaively, you could use choice items with Blue Flare, Draco Meteor, Fusion Flare and Dragon Pulse. It's STAB combination is unresisted, even by heatran.

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Zekrom is good as well - not as good as Reshiram in my opinion, but still... A choice band/scarf set of Bolt Strike, Outrage, Fusion Bolt and Dragon Claw is probably your best set.

Also good are Hydreigon - Dark Pulse/Dragon Pulse/Draco Meteor/Focus Blast, Haxorus - Swords Dance, Dragon Dance, Earthquake and Outrage or dragon Claw, and Lucario - Nasty Plot, Dark Pulse, Aura Sphere and Extremespeed or close combat, swords dance, extremespeed.