Here is my honest opinion--and I have only flown HP first class about 5 or 6 times.
HP serves Kirland water--cheap. They also serve Diet Dr. Pepper which I love. When I was flying HP/US, US was just stopping the greek scrambled eggs, so although minimal like US, HP's meals were slightly more edible. There is no snack basket on the HP flights. I usually do not eat from the snack basket, but on long flights, a cookie is nice now and then--particularly because of the lame thing they present as dessert on these flights. I did like the fact that the movie changed on HP mid-month. Both US and HP planes are filthy. I like the FA's slightly better on the East side--particularly an old (and not in a mean way) PI FA or Travelpro72 when I fly PeoplesExpress. I will not drink the wine on US or HP--I'd rather have gasoline or a vodka/tonic. The limes on HP were green. I'd say its a tossup or US is slightly better.
I don't like the layout of HP planes. The lack of a closet puts you right at the door. The fact that someone stands guard at the galley in the front when the pilot uses the lav is just disturbing--I prefer the cart. I like to mix my own drinks, so I like the fact that US gives you the bottles (but not when they hand you only one). I like the water predeparture on US. And, of course, I always liked seeing a familiar face on US who would inevitably remember a conversation we had.