Definately not Corsola and probably not Carracosta. Corsola is just awful and while Carracosta is good in the lower tiers, it just can't handle OU.
Empoleon and Gastrodon are both great Pokemon and can be used depending on what role you need filled. Empoleon should be used if you need a Special Sweeper, as its Petaya+Agility set is very potent. However, I think there are better Special sweepers for Sand, such as Latios. So Empoleon might be a little outclassed in that regard. As for Gastrodon, it preforms brilliantly against Rain teams, taking Water type hits like a boss. Sun also, as it is resistant to Fire type hits, unlike Empoleon. It is a better wall/tank, and usually it is the best at what it does, taking Water types down. So Gastrodon might be an easier fit on your team.
The choice ultimately comes down to you and your needs.
Movesets for Corsola: http://pokemondb.net/pokebase/4987/what-is-a-good-moveset-for-corsola
Movesets for Carracosta: http://pokemondb.net/pokebase/13113/what-is-a-good-moveset-for-carracosta
