There are two other considerations:
I believe that STN - DXB is once daily by B777, LHR - DXB is five or six per day by A380.
Business class in the 380 is much more fun than in the 777.
Secondly, if by chance you miss your homebound STN connection, you may be faced with the choice of 24hrs delay or a seat going to LHR, LGW or BHX. If you miss a homebound LHR connection, there will probably be another one in a couple of hours.