Stop clans and attack manipulation clans are the most popular
Least used: Berzerk and Frozn
Most used: Sakrohm, Uppers and Piranas
It also depends of the game mode.
Freaks are much used in T1, but very less in T2
Popular Elo clans and cards are the ones that make it into the format election.
In Elo -
Freaks = cause everyone starts with 14 hp so the poison really helps, plus it requires strategy and calculators which is very popular with the more skilled players
Gheist = SOA plus high damage cards and generally better abilities than Roots
Nightmare = SOB plus high damage cards and generally better abilities than Piranas
Huracan = It's new, so few bans and you start off each round with +14 attack
Jungo = Ongh. Just build a whole deck around him and use it on the weeks when he's not banned.
Pussy Cats = DR
Fang Pi = High damage for the 2hkos
There are other clans, but they aren't as popular either because of permabans or because of lack of good deck comp such as bad two stars, etc.
Bangers and Roots are the most neglected clans!
Bangers used to be most powerful clan in the game but they dont ever get any new good cards. The only card they got is Beeboy and he got banned right away. Bangers decks are still using all the same cards from 5+ years ago when they used to be great but not because of higher power level of other cards they aren't good anymore. Blaaster Cr, Vermyn N, Juicy Lord, Graff have gotten outclassed by the new cards but yet UR doesn't give them any new replacements or options.
As for Roots, every good card in their clan is ELO banned! I really don't understand why either. The people that make this game really hate Bangers and Roots