You get Delta benefits as long as you don't fly the E175. There are plenty of Delta trips out of ORD. You don't have to be based in a Delta domicile to fly a Delta trip.

Delta doesn't charge to list for first class, even for international flights. I went to South America recently and it would have been either $56 round trip first class on Delta, or $400 round trip first class on United. Combine that with the fact that United flights are almost constantly oversold and you actually have a chance at getting on Delta flights and there's no comparison.

The hardest part about using Delta benefits for me is that I don't live in a Delta domicile and the leg to ATL is always full.