For whom you think that IT manager should report to?

It depend on the organisation size, in big organisations IT Managers report to Group Chief Information Officer, while in smaller size organisations report to General manager or CEO

CEO

IT Director or CEO

Managing Director or CEO

to  ADMINISTRATION MANAGER

the main job of IT Manager is to faciltate business objectives into it services, so depneds on the organization who ever has the power of Business Processes, IT should report to him/her regardsless of their expertise whether its COO or CFO or CIO or CEO... but in many cases the worst pissble line to report to is CFO...

Is there any best practice, standard, link or benchmark for this to support your answers?

According to the Org size and hirarchy width , could be : IT Director , CTO Or CEO He should work in coordination with the Managing Director , but in some cases he should report ON the MD's technological behavior , and thus should be reported directly TO the CTO or CEO