Ideally, such a site would already exist (sort of FaceMash for designs, or HotOrNot for designs) and would have a large crowd already, which logs in and gets a bunch of random things to vote for. Random with a limit of N per day because we don't want people to game the system by inviting their friends to vote for a specific one.
As other folks called out, this can give you a sense of customer comprehension / stated preferences & reasons why, but may not give you the level of confidence a true A/B test would (launching both iterations & splitting traffic amongst & measuring conversion difference)