You can pre-select exit row seats on US, which partly makes up for the lack of E+. This includes a UA 2P who can't do so on his mother airline.

You find fewer "elites" in Y taking up exit rows on US because the UG allotments are more generous -- CP (the highest level) gets unlimited UGs.

On the Shuttle you can theoretically check-in on the web and select seats up to 24 hours ahead of time. I did it several months ago but failed on my most recent attempts. (System error.)

US started flying mainline 319s with F class on the DCA-BOS shuttle just a few weeks ago. They moved their single class 320s to mainline for low yield Cancun type destinations and consolidated all 319 Shuttles on the LGA routes. However, this Monday they still had one single class shuttle BOS-DCA and I happened to be on that flight.

The single class shuttles (still on flights to LGA) have about 34" pitch. Also, the Shuttle serves Sam Adams beer for free, which I like a lot.

Avoid US mainline Boeings if you can. They are filthy and the pitch could be worse than E-.

p.s. Gold preferred (US2) = UA 1P