Personally, i am not too educated on regional products but JetBlue seem to lead on that? Then for international i would say United with Polaris and Delta with whatever theres is called are leading.
In terms of fleet i like the streamlined Delta fleet of A330’s etc however the inside matters. Apparently also (Sam Chui you better be right) the United Staff can be quite rude at times.
Seen as though i don’t know much about this area, i look forward to hearing about your opinions.