United has Polaris seats on its 787-9 for 60k miles. I've never tried the Polaris seats, and I haven't flown either the 787 or A380.
That's not the Polaris seat on the 787. It's the B/E Diamond in a 2-2-2 configuration.
It's a close call, but personally I would take LH. The UA seat is more comfortable but I prefer LH's service. If service is less important to you, the UA hard product is better, especially taking into account the superior bedding.
If you can fly UA's 77W that's far superior to either.