Rocks Pirates. Just the fact it was consisted of so many current legends shows us how great the group was. Most other crews just kinda... faded, with most crew members retiring and the captain dying.

Kaido, BM, and WB were all on the Rocks pirates and Roger and his crew needed help from Garp to beat them

Rocks pirates obviously. Most of their members became legendary figures

The organisation of the beasts pirates and how its system is capable of controlling such a large portion of the world is frankly incredible, the only crew that comes close to having such organisation would be the Blackbeard pirates.

Rocks pirates. Crew is literal insanity in terms of power.