Where are you flying? You might consider the AS Mileage Plan if you aren't looking forward to too many upgrades because

(1) You get benefits on DL which will give you preferred seating and almost alliance-type benefits, plus some (not much) status on the upgrade list, and luggage allowance

(2) Your AS miles are good on almost everyone that your UA miles aren't good on (AA, DL, and a hodgepodge of good international carriers)

(3) AA may get some additional partner benefits soon. Now there are essentially none.

Between AS and DL, you have a fair # of nonstop - not as good as UA alone, but nothing comes close to UA here. AA is a sorry shadow of its former self here.