I think there are 20 flights or more a day from ATL to LGA whereas there are only 6 flights a day from ATL to JFK.

I think most of the DAL flights are mainline. Not sure what flight numbers are 9E. With ATL opening up as a base I suspect they may have some CRJ flights to NY as well.

The one thing you have to be prepared for is DELAYS. You may land there 30 minutes early and get to the gate LATE.