The second one, if you're powering to 30
The first one, if your maxing
Personally I'd power both of them to 30 instead of one to 40. As to why, Groudon is the best/only ground attacker in the game worth powering up. He was awesome versus Gengar and Ninetails and will continue to be awesome against Mawile, Aggron, Regirock, Registeel, Jirachi, etc.