The videos taken on my phone are so absurdly terrible looking that I dare not try to introduce the artifacts of an additional compression scheme on it.
They'll play on VLC on both my Mac (Quicktime also works; I wonder if Quicktime would play it on a PC? If so, I wonder if you could then export from Quicktime?) and Linux boxen; it'd only be if I needed to authour a DVD that I'd consider transcoding the files. I'd probably attempt first to export it from VLC in that case.
SUPER from erightsoft has been a godsend for video conversion.
Problem is, if the incoming video is poor, no software can create resolution that isn't there.