IMO JetBlue Mint (original product throne seat) & UA true Polaris on a widebody plane are the best transcons. DL on their 764 or A330 are ok. AA F is good too but the price is often far beyond UA & B6 business making it less appealing for the product. AA J is ok too but 2x2 on their A321 isn't as nice as the other options. AA wins on lounge access though whereas JetBlue doesn't have lounges while UA only provides access to the UA Clubs and not Polaris which would be inline for the Flagship lounges.