The most conservative members of Congress are...

A leading right wing group unveiled their rankings of the most conservative members of Congress Thursday, and some prominent Republicans -- including Sens. Marco Rubio and Rand Paul -- came out at the top of the list.

The American Conservative Union's list for 2012 also singled out the least conservative members of Congress, including some moderate Republicans who scored among Democrats.

In the ACU's rankings, which are derived from how members voted on key measures, seven GOP senators emerged with perfect scores: Ron Johnson of Wisconsin, John Kyl of Arizona, Mike Lee of Utah, Mitch McConnell of Kentucky, Rand Paul of Kentucky, Marco Rubio of Florida, and Pat Toomey of Pennsylvania.

Another 34 House members had scores of 100 percent, including Michele Bachmann of Minnesota, Marsha Blackburn on Tennessee, Tom Price of Georgia, Jeff Flake of Arizona and Tim Scott of South Carolina (Flake and Scott are now both senators).

"Their unwavering commitment to our shared conservative principles stands in stark contrast to the liberals in Washington who continue to want an expanded role for government at taxpayers' expense," ACU chairman Al Cardenas wrote in a statement.

Among those liberals were 20 Democratic senators achieving a "perfect liberal rating" from the ACU. They included Senate Majority Leader Harry Reid and the Majority Whip Dick Durbin.

The least conservative Republican senator on the ACU's list was Sen. Susan Collins of Maine, a moderate on many issues who's been re-elected three times. Her former colleague Olympia Snowe, who retired at the end of last year, was also among the lowest-rated Republicans on the ACU's list.

Sen. Scott Brown, who was defeated last year in Massachusetts by Democrat Elizabeth Warren, was tied with Sen. Lisa Murkowski of Alaska as the third lowest ranked Republican on the list.