On what routes, and in what class of service, do you hope to redeem your points/miles for free travel?
Just because you are in Atlanta does not necessarily mean that you have to fly on DL, even though DL surely serves more nonstop destinations from ATL than other carriers.
Whether you would be better off earning miles or travel credits will likely depend on the relative cost in cash vs. miles for the particular flights you want to book.
And even if your paid travel will be primarily on DL, that does not necessarily mean that you must credit those flights to DL: DL flights can be credited to any of DL's Sky Team partners.
Occasionally, offers for the Amex PRG with 50,000 MR points after $2,000 in send will pop up; some people have reported getting it when going to the Amex site from a Chrome incognito browser.