System vs user-assigned managed identity vs service principal

This sheet compares System-assigned MI, User-assigned MI, Service principal, Legacy service principal.

Criterion	System-assigned MI	User-assigned MI	Service principal	Legacy service principal
Lifecycle	Tied to one resource, deleted with it	Independent, attach to many	Independent app object plus SP	No app object, single tenant

The verdict, the full comparison, 6 rules and 3 traps are part of SC-300 access. Unlock SC-300.