Dear Expert,

Please help to recommend me the commercial certificate for exchange server 2013.

Thank you in advance.

This is not a black and white statement. You need to look at the security policy, CRL publishing and support that you get. Additionally you know the devices that you have connected to Exchange so based on that choose an issuing CA that is already in the trusted store of the devices.

Dear Expert,

Please help to recommend me the commercial certificate for exchange server 2013.

Thank you in advance.

Go for Digicert or Godaddy or VeriSign or anything but make sure you buy an EV (Extended Validation) Cert ...

All the best.