Knight Capital Group (NITE) used to be "one of the worst and one of the dirtiest," said Jim Cramer on CNBC's "Stop Trading!" segment on Thursday. Then CEO and Chairman Thomas Joyce came on board and "turned the place around. It's a remarkable firm. It does great business."

Cramer called Joyce "the most honest guy alive" and "the best there is."

He sang a different tune about Treasury secretary nominee Timothy Geithner. "For months, I've been saying Geithner's the wrong guy," Cramer said. "Now everybody's discovered the truth. He's all yours."

Cramer said that even if Geithner wouldn't have been his pick, it's too late now, and it's more important just to confirm him and fill the empty position.

"Everybody on Wall Street who lost billions of dollars loves this guy," Cramer said. He said he knows Geithner's "a great public servant" but that Cramer's lawyers told him, "'Jim, if it was you, be prepared to go down.'"

At the time of publication, Cramer had no positions in stocks mentioned.

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