Best app coverage and the easiest automation tool to adopt
Zapier is the broadest automation platform by a wide margin and the easiest for non-technical staff to adopt. Its per-task pricing is the most expensive in the category at volume, which is the trade for that coverage.
Best for technical teams needing self-hosting or high volume
n8n is the technical team's automation platform: a capable visual builder that lets you write code where needed, and a self-hosted edition with no per-execution cost. Setup and maintenance are yours to own.
Pipedream is an integration platform aimed squarely at developers: prebuilt components where convenient, Node, Python, Go or Bash where not. Enormously productive if you code, largely pointless if you do not.