That is a good question. And after thinking about it I'll answer with a proposal. How about - in addition to Module Reviews - we add a module voting section to PerlMonks. Only modules that have had a vote appear. Then you can search by vote - or first search by function and then compare votes. Modules within a certain category would have a comparable relative vote (popular categories have many votes and less popular have fewer relative votes).
Also, possibly in the reviews, have a section for listing comparable modules - and how or if they compare.