Hello,
The comparison between modules with similar functionality is very useful to decide on which module to use. There are several documentation pages and discussions about such comparisons.
Examples:
Module comparisons (only modules able to upload to remote server)
http://drupal.org/node/567432
Comparison of Glossary-type modules
http://drupal.org/node/1179172
Comparison of HTTP Client Libraries
http://drupal.org/node/266511
Comparison of HTTP Client Libraries
http://groups.drupal.org/node/233173
Comparison of node / entity references and relationships modules
http://groups.drupal.org/node/213528
Comparison of Node Ordering Modules
http://drupal.org/node/398508
The problem
Such pages are scattered in the Documentation and Forums of Drupal.org.
My suggestion
It could be more efficient to add a comparison feature to the Modules interface of drupal.org.
For example, in addition to "Related projects" block on the bottom of the right side column which may sometimes show irrelevant modules, it could be extremely useful to provide a block including a list of modules that do similar functions to the current viewed module, with a link to a page of automatic comparison between them, or at least, to an manually-authored comparison page like those mentioned above.