“So when Newt changes his ways he’s seeking redemption and learning from his mistakes, but when Santorum does, he’s to be condemned for his older vote.”
No, they all do it to some extent, but Gingrich’s record is just much more consistently conservative.
American Conservative Union
100% - Gingrich: Annual 1998 ACU Rating (90% Lifetime Rating as of 1998)
88% - Paul: Annual 1998 ACU Rating (88% Lifetime Rating as of 1998)
84% - Santorum: Annual 1998 ACU Rating (83% Lifetime Rating as of 1998)
88% - Paul
84% - Santorum
So your second choice is Paul? Or perhaps Romney? Almost by design, the House is more partisan and adversarial than the Senate, which is inclined to be more conciliatory and compromising. By '98, Santorum had been in the Senate for three years. It doesn't surprise me one bit that a junior Senator (particularly one from a state like PA) doesn't have a higher ACU rating than two Representatives from safe conservative districts. I'd frankly be quite surprised if he did.
Also, if you look at the vote criteria employed by the ACU for that year, one of the House votes considered was their impeachment vote, which was a pretty clear vote for anybody even remotely conservative. The Senate votes evaluated by the ACU that year did not have a corresponding "gimme." That all said, if you look at Rick's lifetime rating after his last year in office 88.1% for a Senator from a swing state, as opposed to Newt's lifetime rating of 90% for a Representative from a conservative district, the difference is, to an intellectually honest person, negligible.
But as you pointed out earlier, we can hold Rick's old bad votes from '98 against him, but anything even remotely un-conservative that Gingrich has done since '98 should be considered water under the bridge.