Apple TV or Mac Mini?
brk: I have several of each running for the same application.I'd recommend the Mini.  It does everything the ATV does, and much more, for not a lot of extra $$$.The ATV is a nice little device, but you're fairly limited in what you can really do with it (no Netflix streaming, for example).  One nice this about the ATV is that you can stream audio TO it from iTunes on another machine, I use that feature a lot.