622a3669___FetchXML_reports_in_CRM_2011__SQL_Reports
[0] Flexibility [FetxhXML Reports] Functionality is restricted to what the Report Wizard can support which can be quite limiting at times. [SQL Reports] 
These reports can take data from CRM and present it in multiple ways. Reports can achieve complex requirements as you can use any feature from SQL Reporting Services.
Gonzalo Ruiz - Dynamics CRM: SQL vs. FetchXML reports in CRM 2011
SQL Reports