No, none of these Pokemon are Ubers, although Garchomp can still function great in Ubers due to it's Speed Stat. Haxorus and Garchomp are OU, and Charizard is NU.
There isn't really a best Dragon, but the one's that have always been my favorites are Salamence, who can pull off an amazing mixed set, and Latios, who has great Speed and Special Attack.
Hope this helps. :)