UA international flight
 

From LHR to LAS Boeing 777 with E+ Access, which seats are going to be the best in that class? I have to call to get my seat assignment apparently!

You should be able to log in to your itinerary on the United website with either your Mileage Plus number or record locator and change your seats (it might take a few days from the time you purchase E+ Access). If you have any trouble, call. Just don't wait for check-in. As far as best seats, check the seat map for your flight and then seat guru. There are a couple of different B777 models. With an E+ subscription, you can select anything that's available except exit row seats.

United doesn't fly B777s to Las Vegas, so I assume you're connecting somewhere. Almost all United flights to LAS are on Ted, its not-so-low-fare brand. Ted flights are on A320s with an E+ section, no first class cabin, overhead screens and buy-on-board snack boxes.

Connecting where, by the way?

Seatguru.com

Connecting LAX on the way there and ORD on the way back.

Like ms_go and Gardyloo says, just check seatguru.com.

LAX-LAS and LAS-ORD are on the TED Airbus 320 (32S).

Most E+ seats are okay, since you have plenty of legroom, so it's not as crucial to find THE BEST seat. Just avoid those with limited recline or whatever reason seatguru.com gives them yellow or red.

You can select your seats online, as ms_go indicated. Is your E+ Access linked to your Mileage Plus account?

When you select your seat online at united dot com the E+ seats are shaded blue (rows 1-11 on LAX-LAS). I avoid row 1 and choose aisle seats. But you might want to get a seat on the left side, seat A, because when you fly into LAS from LAX the plan goes east, south of the city and you have a great view of the entire city including the strip, then it does a u-turn and lands (after it makes the u-turn there is a view from the right side of the strip).

Actually, the A seat is good for departing LAX, too. The plane flies west out of LAX and then makes a u-turn and flys just south of Long Beach. You have a marvelous view of L.A. at that point.