I concur with those saying to choose the 747-400 option. Although it's an older aircraft, all of them are identical in WT and all have AVOD. The 777-200s are a very mixed bag at the moment. So far only one has the new WT cabin and Thales AVOD system as on the -300ERs. Of the rest just over half have the Rockwell AVOD (the same as on the 744s) and the remaining ones have the old GMIS IFE system (which is still seatback but is a tape-based 12 channel selection). So unlike the 744s, there is no guarantee as to the IFE you can expect until you board.

From memory, the GMIS (12-channel loop) 777s are: ZZZA-C, VIIA-N, VIIS
the Rockwell AVOD ones are: VIIO-R, VIIT-Y, YMMA-U
the new WT and Thales AVOD are: RAES