GOP rankings have Palin and Reagan as moderates and Rand Paul as the most conservative of the bunch, but wait !!! There is more:

13 share

poor reader interest

Key to reading this chart:

The higher the score,  the more conservative the candidate.

Using Goldwater's voting record as the benchmark for conservative measure with a "67" score,  we have the following:

Rand Paul scores 98,

Paul Ryan and Marco Rubio both score 57,

 Cantor scored 55,

John McCain scored a low 38.

As it turns out,  Sarah Palin and Ron Reagan are/were much more moderate that some of their GOP counterparts,  including Marco Rubio and Paul Ryan.  George W was considerably more conservative than his father.

If you understand a "50" as a combined score (far right column) is a strong conservative,  you see the top ten GOP candidates include many of the more recognizable names within the GOP.
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Chart courtesy of FiveThirtyEight,  here.