Honestly, if much of your travel will be to DC, SF, and Chicago, maybe it makes sense to stick with United? Those three cities are all hubs, and LGA has lots of daily departures for both DC and Chicago. SFO and AUS will require a connection on any airline at LGA. CLT and MIA would be nonstop possibilities on AA, though.

From what I've heard and read on FT, DL has been an utter dumpster fire this year due to staffing-related operational issues.

Maybe you can request a status match and give the different airlines a try? For me personally, LGA has always been a much easier airport to fly in/out of than JFK, even before the reconstruction. While DL's T4 at JFK is quite nice (yay Shake Shack!), I wouldn't go out of my way to choose it over LGA if that meant significantly more travel time. Especially at a time when they're having major reliability and customer-service issues.