To be honest, there are really no ''best'' clan's here, they have difference as we think of Skill, attitude, and of course their Meaning of the clan.
My top 5 Attitude clan list:
(eVo)/(Tur) : their way of Recruiting, being alive still!, and how mature and Polite they are, they have an 10 from me: Skill level(10)
|FA|FallinAngels) : They have a great server that they have been keeping up pretty long, They have alot of funny maps, All of them act mature and are great people that do not abuse/griefing/Aimboting/etc, They have also keept togheter a pretty long while, being inactive, but do also play alot of other games: Skill level(Ok)
=V=Venergetic) : Pretty good guys that doesn't play anymore, still they have been around a good while, they have always been nice, and still are

Their act and gameplay is Making me proud, they sticked togheter as 1 clan, LOONG, and wll be remembered: Skill level(Profesional)
CU|) Probably the oldest clan now, they are still alive, And got plenty of members, they've been an Nice clan, members had respect for others, CUdyin have keept it togheter and will keep it

They have proved their attitude, acted like real people, not been Griefers/aimboters/etc, they got a 10 points from me

as they Had fun, great members, and alot tho

Skill level(Profesional)
{SGA}, They was a great clan, great people, great Gameplay, can't say they really was any addicted to the game as they had alot of fun tho, they have my respect for Holding so strong, Great leaders aswell

They are probably one of the times best Clan/Members/Leaders/Attitude/Polite/Skill, Skill level(Profesional)