Res_fax or app_fax? with spandsp, Asterisk 13+

I found that to send or receive a fax, I have a choice of res_fax + res_fax_spandsp or app_fax. Tried both and I successfully heard the fax sound with both modules.
Which one should I implement?

Thanks in advance.

Version: Asterisk 13.22.0/ Centos 7.5

The res_fax module with res_fax_spandsp is the supported mechanism. The app_fax module is deprecated and may not exist in future versions.

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Thank you. I missed the following on the wiki.

The app_fax module has been deprecated in favor of the res_fax module and
the new res_fax_spandsp backend.