Which video format would be most suitable for Video Streaming from server to Android Tablets and Android Mobile phones?
.3gpp or .mpeg4?
It depends on compatibility; there are specific format which are supportable, nicely mention at developer site, have a look:
Android Supported Media Formats
For video content that is streamed over HTTP or RTSP, there are additional requirements:
For 3GPP and MPEG-4 containers, the moov atom must precede any mdat atoms, but must succeed the ftyp atom.
For 3GPP, MPEG-4, and WebM containers, audio and video samples corresponding to the same time offset may be no more than 500 KB apart. To minimize this audio/video drift, consider interleaving audio and video in smaller chunk sizes.