Which airport should I fly out of?

I’d guess that it’d be cheaper to take a low-cost flight to London, and from there the flight to the US. Just make sure there’s more than enough time between flights, since delays are not unusual, and neither airline would be liable if you missed your flight.

It really depends on what the savings look like. I did the stop at london track when I was on my way to Rhodes, and it was totally worth it. (800$ cheaper)
but if you could find a more direct flight, less stress plus more time spent at your destination.

Is there a Delta-Airport near you…? So you could fly via ATL.