Seat layouts are obviously different - but service should be the same (in terms of catering and drinks) subject to the calibre of the crew.
Some Gatwick based 777s have not yet been converted to the New Club World and World Traveller Plus configs and therefore have Old Club World cradle seats instead. These are all planned to be converted by mid-2004.
So it mainly comes down to which seats are best on each plane. Check out :
www.seatexpert.com
www.seatguru.com
For maps of 747 and 777s - with helpful added notes telling you which seats are best.