You're basically screwed
UA you can get your upgrades at higher fare, but if you can go JFK-SFO then at least you could use upgrades for PS service.
DL you have the same issue.
DL economy comfort and service I rate somewhat higher than UA, but UA has a lot more room in E+ for most flights. And MP still somewhat more valuable than DL for redemption.
All in all I'd vote United, or give up on both of them and put your miles on AS or Virgin.