Looking for the best plugins (systems) to fully utilize Infusionsoft API

I’d like to know what are the best plugins/systems that works best with Infusionsoft API. For contacts/database management, sales and marketing, and automation?

I recommend you take a look at the Marketplace: Keap Marketplace

The popular items will have a higher number of reviews.

My favorite tech stack includes:

PlusThis - for very ‘Keap-centric’ tools
AppointmentCore - for scheduling (tight integration with Keap)
Integromat (now Make) - for all other misc 3rd party integrations
InfusedWoo - if you are running a WooCommerce shop on your WordPress site