OK so the review sites are certainly great for improving your click through rate and influencing your customers etc, but do not assume they will benefit you totally.
Review sites (see list of google approved partners here) only automatically benefit Google adverts (CPC) by default and you will need a minimum number to qualify for the star rating. You may get a boost from a high traffic and quality review site organically but like Garrett says - opt for a review site that meets your needs and is also frequented and trusted by your users.
Should you wish to benefit from star ratings in the organic results you will still need some technical knowledge to apply aggregate ratings schema to your site and even then it is not guaranteed they will show.

