I would take Swiss. The service is more consistent and delivered in a more caring and individual manner. But I suppose I should ask which type of aircraft you would be on. UA still has several different flat bed seats. If you get the old United (not Continental) aircraft the seats can be very crowded. It’s ok on the 767 but the 777 and 747 main deck are very crowded with 8 abreast seating and no real privacy dividers. The crews are all being retrained on United and I had a great flight on UA a month ago in international business but a rather mediocre return so the service is a bit spotty still. The US carriers are upping their game and are not as bad as they once were. But I still much prefer Swiss to any of the US offerings.