I don't think either of those planes has bad C seats. "Regular" A350 row 1 has wider foot area. Row 6 might be a bit close to the toilet. Row 1 and first eco row behind 9 have bassinets. Bar between row 6 and 7 is usually no source of noise. Middle seats have no vents. I personally pick window row 4 or close to it, but don't sweat it if you get another seat.
A380 first row (10) has bassinets, no Y bassinets in hearing range anywhere. Seats in the rear are close to the bar, but while the bar gets used much more than in the A350, not much noise makes its way into the cabin. All window seats have limited views due to the massive wings, but gorgeous extra storage on the window side (typical for A380 upper deck).

All in all I think QR did a great job providing comparable comfort for all seats across the cabin. The only seats of the same design that are clearly inferior are those in row 6 on the 787.