Between Singapore and London SQ only operate A380 and 777-300ER (77W). Some of the 77W's have older seats on IFE, although I think London has been upgraded to newer products on both 77W flights. Note: they do not operate any older (retrofitted) 777-200's or 777-300's on the route so I wouldn't worry too much - these are the planes that do have lower standard IFE and in some instances lower standard seats. However the 77W and A380 both provide good seats and good IFE (older and newer versions). Some people prefer the A380 because the plane noise is quieter and cabin atmosphere better (less dry) than the 77W, but it can be difficult to notice unless flying regularly.

For the SIN-CGK sector you could any sort of aircraft, but the sector is not worth worrying about the aircraft type, as it's only about 90 mins in the air.