I’ve tested both of them and cleary there is only ONE winner. But this will come later.
How Rich Snippet SERPs work in general
You use Metadata in your HTML to present the ratings to Google. Google takes them if they like to and add them to their results for you website. I’ve noticed, that mostly the popular posts get the stars fast in SERPs.
WP Review or WP-PostRatings, which plugin gets the job done?
I had some trouble with WP Review which I couldn’t solve.
First it had layout issues with the second plugins I am using on my projects called Table Of Contents Plus and secondly the Structured Data Testing Tool | Google Developers showed me the error “no rating object given” so it seems to me that this plugin does NOT work at all.
The winner plugin?
Clearly WP-PostRatings for me.
It gives you settings for almost everything you need and I’ve got my star SERPs within one or two days on my popular posts.
Just don’t forget to enable the Google Rich Snippets after the installation
Do the stars in SERP help with traffic?
Hope this helps and have fun