"I would say they are up there with the best New Zealand sides I have faced," said Williams, who wore the No7 shirt in Wales' 29-9 defeat at the Millennium Stadium last Saturday.
"They are efficient in everything they do and it's difficult to find a weakness."
Warren Gatland's men led 9-6 at the half-time interval but the Kiwis showed their class to run out convincing winners in front of a sell-out crowd.
"They are not afraid to take chances and kept threatening us throughout the match," added Williams.
"Eventually their pressure told. Once they got momentum, they didn't look back. They took their opportunities and we didn't take ours.
"They breezed past Scotland, breezed past Ireland and breezed the second half. They are a class side, and you wouldn't bet against them beating England and getting the Grand Slam.
"But we only gave away two chances against a top side. That's the best we've played this autumn and we are not a million miles away from them."