to this previous post the all stars are not the "worst clan" as everyone has thier own playing style and this can broaden the range on what is considered the "worst clan".
It also depends on what game mode you are playing, for elo you need a solid deck of either 4/4 cards or just a straight up full deck of a single clan, then there is a range called "splashing" which consists of have 7 cards from one clan and having 1 card from another. popular choices are Spaighi and Lehane.
Survivour has resulted in "the bigger the better" with cards such as guru Cr and General Cr playing major parts and also to make it the best have the games biggest damage reductors (graks and uranus)
but the anwser the question "what is the worst clan?" there isn't one, but don't pick sakrohm because uppers are better and don't pick berzerk because freaks are way better.