I'll kind of add to what @edg says. Recent accomplishments evaluating and selecting software or frameworks, experience with the frameworks you are evaluating (as well as a well rounded view of frameworks in general), and political and social adeptness are important. If the environment is political, then the social and political adeptness carries equal weight in my book. Also, if the audience for the evaluation is non-technical, then they have to be able to explain techy things in non-techy terms.
You are also looking for a consultant, not a contractor. A contractor does what you tell them to do. A consultant works with you to come up with the best solution for your business needs. There is a distinction.
EDIT: experience in your particular industry would be important as well.