UA. You'll be on a 744. They're pretty ragged around the edges. Jam-packed 2-4-2 downstairs, a more civilized 2-2 on the upper deck. No direct aisle access so you either have to climb over or be climbed over for lav access. Seat itself is pretty comfortable, AVOD is decent. Food and FA service are highly variable, from not very good to reasonably ok. Wine and liquor selection is poor. 744s are not particularly reliable, lots of mx delays and cancels.
SQ: The 77W. 1-2-1 in J. Beautiful cabin, a much more luxe setting. Seat is very wide and private, though tall people can find it uncomfortable and it's a pita to turn into a bed. Food, service, beverages, and AVOD all several cuts above UA. A much more luxurious experience all around. Overall, more reliable than UA, except you're not in a hub, so if something goes wrong there will not be a spare aircraft handy.
Really depends how much value you place on the extras you would get with SQ.