All good comments. I travel this route 3x per year and have taken all possible routes. The LAX/SFO routing is more expensive for the H or C fares that I have taken. My thoughts.

1) via IAD gets you more miles, 5129 via IAD, 4841 via ORD. Do not book the single flight number as you will only accrue the non-stop mileage of 4670.
2) LH via FRA and MUC in C or F are great, not in Y. More miles, but no UA metal.
3) I have routed via SFO several times on the way home by asking for it as my scheduled flights were full.
4) Customs are mucch easier at IAD via the mid-concourse instead of the train ordeal at ORD.
5) Plenty of 777 connections from DEN-ORD and one to IAD (1015) for the two 1800 hour departures.
6) The IAD flights seem to fill up faster.

Enjoy