As others have said, do direct- either UA or B6 (JetBlue). The 757 lie flats are perfectly comfortable on that route. The 777 you're referring to as "Polaris" is a pretty neat plane to fly up front domestically, and I would attempt to book it if it were flying from whatever your most convenient airport is...but it's ABSOLUTELY not worth connecting considering your current option is solid. If this were a 737 first product, I could see a slight hesitation- but I still would opt for the most direct.

Coming the other way on a red-eye, I'd probaby feel differently. The hard product of the Polaris style seating is great, but connecting BOS-EWR-LAX is guaranteeing something in the matrix goes wrong lol.