Integrating with 3rd party app

Integrating with 3rd party app

Hello World,
I have recently signed up for a Zoho. 
I have reasonable experience in SFDC and I trying to apply my SFDC knowledge to Zoho.

Problem:
I am trying to integrate a couple of 3rd party apps into my Zoho CRM custom module.
It seems there are a lot of options like Extensions, Custom Functions, Zoho flow etc.

Is there a checklist or best practices available to help me decide the best option to choose from ?

Thanks,