Well, you only have one choice: United. No other airline offers non-stop (or one-stop) SFO-IAD services. There are eight dailies, all handled by various A320s, 752s, 762s, 772s, and 763s. If you want an early morning flight, one leaves a 6.40, but it's an A320 flight (UA180). If I were you, I would take the 7.55 flight (UA170) on the 763, or even better, flight UA946 on a 772. I personally have never been on a UA 777 or 767 (I almost always take the national carrier when flying international), but from what I hear, they are very nice (what 777 isn't)? If you get an international 767 (quite likely). If you want to make a connection (which, for an airplane spotter, can be fun), there are plenty. USAir via PIT, AA via DFW or LAX (either which would be ridiculous, although LAX is great for spotting!), DL via SLC or ATL (another ridiculous connection!), CO via MSP, and UA via DEN, PHL and ORD. All in all, my suggestion is UA946, the early morning, non-stop 772 flight. You'll enjoy it.