I’ve flown ET a few times. They are an okay airline. Fares are pretty good, they keep time often enough etc etc. Seats in J are bog standard, straight from the manufacturer. The local Ethiopian meals are a novelty, but route dependant I believe.

EK is a much, much better airline. You’ll get Chaffeur drive at IAD on a paid J fare. The seat IAD-DXB will be superior to ET’s. If you get an F fare, the DXB F lounge is well worth the extra time. I haven’t been to the J lounge in many years, but I believe at least one has been renovated. You’ll get an older 77W on the DXB-ADD, but (and some on here will disagree) I think that J seat is still better than the even the best ET seat.

I think the overall EK experience is far more polished and refined. I often fly from South Africa to West and East Africa via DXB, so in my opinion EK is worth the extra time.