It's fragmented.
Tancredo is indeed the most conservative, but he's also something of a loose cannon (advocates bombing Mecca). He's a supporter of the recent full legalization of marijuana.
Beauprez is one of 2 "establishment" candidates, though he has been reliably conservative 90% of the time. He's pretty old and looks it.
Mike Kopp has a compelling personal story, good experience in the legislature, and is a "3-legged" conservative (Defense, fiscal, social). Probably the best public speaker of the four.
Scott Gessler won the most votes at the GOP biennial State Assembly, currently Secretary of State, has fought hard against the Democrats attempt to trivialize ballot integrity (without which we probably would not have recalled the two anti-gun State Senators we replaced this past year.
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US Senate seat:
Cory Gardner is running without serious opposition for US Senate to oppose Mark Udall in November. Seriously conservative, a 92% ACU rating, he's from Eastern Prairie farm and ranch country, gave up his Congressional seat to reun for US Senate. Good looking, and like Beauprez, he loves his cowboy boots.