I googled "jetblue blue vs blue extra" and this page was the first result: https://www.jetblue.com/flying-with-us/our-fares

It has a great table that clearly explains what each fare includes (and what each does not).

As AutoSlash shared, Blue Extra has free SDC and priority security in addition to early boarding, and does not include EMS. Note that if you have PreCheck, you wouldn't be using the priority security lane anyway.

-J.