NAS, WHS, or Linux Server? Whats best for me

Heres the deal. I have 2 primary needs: automatic backups and the ability to share files (lots of media including HD video).

Of course my objective is to centralize access to my media and files and also to automate backups of possibly a few computers on the network. Outside of this, remote access to my media over the net would be nice, but not that important.

It should go without saying i want the cheapest and easiest way to do the above. Id like to "set it and forget it".

So far im considering a premade/retail NAS system, either a retail/homemade WHS system, or a homemade Ubuntu Server system.

Ive done some mild research on NAS, alot of research on WHS, and know almost nothing about using linux as a server (have used Ubuntu desktop). So far to me it seems a homemade WHS box will be the ideal combination of ease, affordability, and power. However im basing this assumption on possibly a biased standpoint.

In your opinions whats the easiest and most affordable way of doing what i want? feel free to post elaborating on your vote