There is great reason to choose Water/Dragon and that reason is Zapdos, and no weaknesses in the top 10. Most Zapdos have HP Grass, Heat Wave, and TBlot. HP Grass and TBolt are now neutral, and you get a x4 resist against Heat Wave. Pyroak also now has to chance against it with it's Fire stab x4 resisted.
Against Stratagem, it wins.
Against Zapdos it wins.
Against Heatran it wins.
Against Fidgit it wins.
Against Revenankh it is a toss-up.
Against Syclant is a toss-up.
Against Tyranitar it wins.
Against Blissey is dependant on Physical/Special bias.
Against Scizor it wins.
As you can see it wins against most threats, has no weaknesses to the top 10 for exchange with more neutrality. I see the no weaknesses as a more important issue. This is the only typing that can deal with Zapdos other then Water/Electric and that typing gets hit with a ground weakness.
Pretty much why I was vouching for Water/Dragon, it will hold off with everyone, it doesn't have to be everyone but it holds off 8/10 in that list.
It decentralizes the top 10 listed.