I had a similar choice. I interviewed and passed, was offered a job as a SA with the FBI, but decided against it. I sometimes regret it, sometimes not.

Are you really familiar with the type of flying the Feds do? It is quite boring. If you eventually go to the G5, you will almost never be home. Forget about things as "min rest," etc. If you maybe want to have the option of flying, and do something else there, it might be a good option.

But first, before you even ask about "which should I choose," you need to have 2 options available. Do you have a Delta interview? If not, you have no decision yet.

Pass the interviews.