I have to say that I have been using delta during the last 7 years for non reving as other airline employee... and for me they are the best.
They have always treated me like their best guest.
Dont be afraid using delta, but i would recommend to always have back up plans in other airlines as well.
The problem with delta in summer is that everyone want to fly non rev with them, and there are larggge amounts of standby people in every flight.
The good thing is that almost the rest of airlines does nothave that long stanby queue, so if you do not get on delta, go to other carrier.
I also want to get to the point that it is very important to list yourself before check-in, as it helps very much at the airport.
And yes, sometimes Delta has treated me very very very well.