For Audio, PowerAmp is the good choice. The only rival I can count here is PlayerPro. PlayerPro can provider bigger sound for the earphone, it also searchs and embeds lyric better than PowerAmp. The combination between PlayerPro and Equalizer app can make nearly the same PowerAmp. yet PowerAmp can handle many file, for example FLAC, but for smartphone at the moment, flac is a heavy thing to be storaged (>10mb/song). So converting to mp3 320 kbps is a considerable and wise move; thus when our music collection is 100% mp3, PowerAmp is nearly the same as PlayerPro + Equalizer.
I choose PowerAmp at the moment, but still keep PlayerPro for searching and embedding lyric to the mp3 file.
For video player, MX is the best choice, it strongest rival is Vplayer, I cannot find many difference between these two, so I keep which one I found first. Right now I'm using Vplayer.