OZ J is far superior, assuming you get an aircraft equipped with the QS (Quadra Smartium) seat.

OZ offers direct aisle access, unlike UA, which is 2-4-2 downstairs and 2-2 upstairs. The OZ aircraft are newer and overall much nicer. OZ's food and service are light years better.

IMO, the only area where UA has a meaningful advantage is AVOD (and arguably safety, but I'm not gonna go there).