The Airbus A320 is the mainstay of United's domestic US fleet, with nearly 100 of the planes in service -- more than any other type. You'll find it on many routes from United's hub at San Francisco's SFO airport that connect to and from Australia flights.
There are three rows of first class, similar to domestic business class in Australia, at the pointy end. You'll be booked into these seats if you crossed the Pacific in business class.
Economy Plus stretches behind first class for another six rows in front of Economy.
Economy Plus is regular Economy seats with a few inches of extra legroom, not proper Premium Economy. It's given out for free to elite tier frequent flyers, or for a fee to everyone else.
The first class cabin
United's first class cabin on the A320 contains twelve seats in a 2-2 configuration across three rows.
(Note that United's seat numbering changed earlier this year as part of its merger with Continental. Whereas first class used to be seats A & B on the left hand side of the aisle and C & D on the right, it's now A & B on the left and E & F on the right. So don't get caught out if you haven't flown United in a while!)
Seat pitch -- the space between your seatback and the one in front -- is 38 inches, which is standard for a domestic business/first class seat or international premium economy.
You'll find overhead video screens rather than individual entertainment screens on United's A320s, so make sure you bring something to do on the plane.
The best seats on the plane
1A, 1B: on some of United's A320s, these bulkhead seats have a few inches of extra legroom, since the wall in front of them has a small nook to give you a bit more space. (You won't find this extra space on all planes, but you've nothing to lose by choosing these seats and hoping for an extra-legroom plane.)
1E, 1F: while they're lacking the extra nook of the other seats in row 1, avoiding someone reclining back into you is a big plus.
The worst seats on the plane
Row 3: although the nice thing about having Economy Plus behind first class is that the passengers right behind you are less likely to be screaming babies, it's still possible. So pick seats further forward in the cabin.
Also in our Best Seats series: