The best practice for integration

I am straggling with my team on choosing the approach we should choose in integrating on-promise Dynamic CRM with other companies and third-party software and systems, we use in our company.

Concerning this msdn page: https://msdn.microsoft.com/en-us/library/dn932127.aspx we have some options. But my team members want to implement integration through service calls to external systems inside plugins.

I want to know what are the pitfalls in plugins approach in integration with external systems ?

Thanks