If you can get a flight operated by Continental with their 752 (*not* 753), you’ll have their lie-flat bed. Looking at the timetable there’s one of those per day, the rest of CO’s EWR-SFO transcons do not have lie-flats.

So I’d go with either that or the UA ps service. Note that UA ps only has lie-flats in F, not C, so CO may be cheaper as you wouldn’t be paying for F on a three-cabin plane.