Getting to LGA isn't too bad - I used to commute to and from NYC and CVG. LGA worked out best for me, but JFK was not too tough either from CVG. There are busses every 1/2 hour from LGA to JFK for $10. EWR is a little harder - you can take a bus from EWR to Grand Central (NYC) and jump on the JFK bus there - both busses are "non-stop".

CVG had lots of options to NYC each day, but I think ATL would have more.