Ok, Groudon's got very nice Attack AND Defense, and I see you use it as a tank(am I right here?).
Anyway, if you are making Groudon a Tank, go with Bulk Up.
Or, if you want to sweep, then Swords Dance.
Also, Groudon has a Massive attack, and you may KO your opponents with Attack raisen 1 stage only,and it would be unnecessary...
Personally, I'd go for Bulk Up, making it more difficult to take down with Physical Attacks, and then hitting Hard , as a Tank should...
Rest is up to you..
Hope This Helps :)