Early action lets you apply early and hear back early without committing. Early decision is a binding agreement to enroll if admitted, and it removes your ability to compare aid offers.
When early decision helps
You have one clear first choice, you have visited, and you have run its net price calculator and can afford the estimate. Acceptance rates for early decision are often two to three times the regular rate.
When it doesn't
If aid will decide where you go, do not apply early decision. You can be released from the agreement if aid is insufficient, but you will have lost the early rounds elsewhere.
Restrictive early action
A few schools forbid applying early anywhere else. Read the fine print before choosing a round.