As far as I can tell, Eliezer picked C.I. to minimize the cost of signaling his views about cryonics, not because he thought it was better than Alcor. See this comment.

See the comment below: My primary reason for signing up for cryonics was because I got sick of the awkwardness, in important conversations, of trying to explain why cryonics was a good idea but I wasn't signed up for cryonics.