I'm checking possibility to convert CRM with Drupal.
Which is the best recommended CRM combined with Drupal?
If I understood your question correctly, you're asking what is the best CRM module for Drupal.
As far as I know, there are a few modules that provides a complete CRM experience out of the box:
Also, go through the nodes categorized with the "CRM" term as they might lead you to previous discussions and/or recipes on how to build it:https://drupal.org/taxonomy/term/36462
Other than that, you can achieve CRM-like functionality by using various general-purpose modules, such as Views, Rules, Entity, References, Profile2, Admin Views etc.
I suggest getting familiar with these modules first, then project what kind of CRM you need and compare what can you achieve with them.
Personally, I'd go with the general-purpose modules as they allow you greater range of flexibility and you still won't have to write code; but this depends on your requirements really.
Hope this helps.
Also check out the CRM group and the ERPAL project.
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