Haven't flown the 748 but some of the points are kind of obvious:
Space: 747. Nothing beats 8 seats on the upper deck. 748 has a lot less space per passenger.
Seat: 748. Same seat as on the A380 and better than the refurbished 747 seat.
Bed: 747. Bed beats seat with mattress.
Knowing that the 747 is only an interim solution, you should only watch out for old F.
My 5 cents.