There is no best clan. If there was everyone would be playing it.
There is no best clan every clan has their weaknesses and strength it's how you use your clan that counts
I would say the best thing to do is find a deck that you play with the best I always use a mono deck try to build a mono deck first of a clan you like practice playing in elo with it so you can learn how to use your deck , it's always good if you know your deck very well and how to use them . For example my first mono deck was pussy cat clan my 2nd was Fang pi chang clan mono also when you get the hang of using those clans try building on another and testing it out .
Hope this helps