Pure Community: TLP, EOP, Fi, MM, FOE, E, CP, C, AAO, IR, TH, and DP were all solid clans who really impacted the pure community in a good way. Yes, there is more, I just can't think of them on top of my head.
Pure Community Clan Wars ERA: TLP, EOP, Fi, MM, FOE, E, CP, POT, Z, CPR, Havoc, IR, and several others that made a huge impact in clan wars were all good clans in their own way.
Nowadays: 85% of all the clans are just multi-clanning clans, with the exception of the top clans who will always be "Legendary", just because they are still here till this day. However, there is nothing wrong with change, so if people enjoy the way clanning is nowadays, then I don't have a problem with it.
So if I had to pick the worst clan, it most likely would be the LPC and MPC clans nowadays. Back in the day, MPC and LPC was just a term used for clans who sucked, and couldn't compete with the top 1-6 clans. This is my opinion, and I tried my best to not be biased.