Winter I would take the ATL option. Summer either has about the same risk of thunderstorms however the NE does not handle it as well. Personally I prefer to connect in the Atlanta Airport verses EWR.
I doubt it, usually you need to pass through immigration and then you will retrieve your luggage. Then the airline will have an area to re-check for your domestic flight.
Delta in ATL doesn't transfer your luggage automatically. You grab luggage at immigration and then you drop if off for your connecting flight. not a big deal most of the time.
"I’m the Dude. So that’s what you call me. You know, that or, uh, His Dudeness, or uh, Duder, or El Duderino if you’re not into the whole brevity thing.”