Probably MPEG 4.
MPEG 1 is good for films.
MPEG 2 is good for TV (it reverts to something similar to MPEG 1 for films).
MPEG 3 - is there one? - I'm not aware of it.
MPEG 4 is good for high compression applications such as sending things down the internet and tends to give better picture quality for high compression (ie low bit rate).