I've flown in Y (Economy) and Y+ (Premium Economy) on the 747.. and in C (Business Premier) on the 777.

MY take on it is that in C it doesn't matter anywhere near as much which a/c ... seats are the same so it comes down to preferences like "Upper deck on 747" or "Forward cabin" etc... which the 777 obviously can't cater to..

In Y and Y+ I really like the 747 and think (from just having looked at the Y/Y+ product on the 777) that it IS better....

In Y+ I much prefer the 2 seat areas... not real fussed whether upper deck or main deck... In Y I always ask for 65-67 H... that's the aisle seat of the seat pairs right down aft.. where the curve of the fuselage doesn't allow 3 seats....

Have a look at the Seating guide (and discussions) on the NZ forum here and you'll see plenty of opinions....

P.S. Read Lucky's Business Premier trip report... even if you are not going to fly in that class... it's a great read!!!!!!