I use Media Player Classic for 99% of my videos.
https://www.techspot.com/downloads/2260-media-player-classic.html
Unless you want to install loads of codecs, use the latest ffdshow beta. This will play almost any video format you throw at it.
http://sourceforge.net/project/showfiles.php?group_id=173941
Additionally, install Real Alternative and Quicktime Alternative so that you can play Real Media and QT files. If you have to.
I'd avoid codec packs like k-lite. They just add unnecessary bloat to the amount of software you have, and can thus cause conflicts unless you know what you're doing. Why not just install MPC and ffdshow instead?
I do also have VLC installed
https://www.techspot.com/downloads/3562-vlc-media-player.html
I don't find the interface as user-friendly as MPC, but it will also play just about anything you throw at it, because it actually has the codecs built-in. Additionally, if you have a corrupt or partial file (for instance, a half-downloaded file), then VLC is the best candidate for playing it.
Music is a different matter as I need 18 permanent playlists for each genre of music open and accessible in one click. So I use Foobar2000:
https://www.techspot.com/downloads/2258-foobar.html
All the software above is - of course - free. If it's not free it's not worth buying.
/flame
Of course, if you're more more interested in what looks pretty than in technical ability and stability, you could always go for WMP, Winamp, Real Player or other commercial rubbish.
/flame
/me chuckles