The bottom line is that we know UA is introducing a highly competitive, very good product when you have to split hairs to find weaknesses to the very best (an inch or two of width here, table space there), and has advantages that few or none have (fleet-wide commonality, dedicated lounges, high J count, good seats for all types of passengers, etc.).
You can tell the UA started from scratch and took years of research to pull it off. I'd trust that more than airlines whose future plans are all over the place (AA), or another that buys off-the-shelf products that lack basic amenities like a comfortable seat cushion (DL).