I'm a Brooklyn based Delta PM and have had excellent success with upgrades on DL. I love the Transcon JFK-LAX/SFO in BusinessElite and while upgrades can be tough to come by, you can same day confirm for free, so if your travels are flexible you can usually get the upgrade as a Plat (or worst case scenario route JFK-SLC/DTW/ATL-LAX).

Skypesos are not the most valuable miles, but there are some "diamond in the rough" redemptions. Went to the Seychelles this summer for 120k and $200 in J with a stopover in Paris. Delta opens up lots of last minute award space, so if you are flexible, you can make the miles work for you. I find Air France availability to be pretty generous as well. Booking flights next summer, they have tons of availability ex-JFK in business.

Overall, they treat me pretty well. I get upgraded 6 days in advance usually and I find the flight attendants extarordinarily accomodating. I've been on many flights where the FAs gave out two pre-departure bevs and even snacks when delayed. I feel like they really do value FFers and have had the Platinum line bend the rules when I've been in a bind.

JFK terminals are not nice, but there are plans to improve. Overall, I'm impressed with the service and schedules, so I have no immediate plans to jump ship.