Those clans are currently not good in ELO.
Sentinel isnt bad and sak is good when bans are lifted
Eh dont listen to people who say clans arent good in elo you can make any clan work in elo as long as you make sure to cover your weaknesses.
For sak - petra, murray, aleister, uranus, and jautya are the stables
For nightmare - edwin, artus, pan, phyllis, cutey,glorg, and karrion
For Sentinel - tobbie, jackson, havok, melvin, and coby
Doesnt really matter which clans you use just make sure you have a good balance of damage, damage reduction, SoA/SoB, and attack manipulation.