Apple is not FLAC-friendly as they have their own proprietary codecs. Neither iTunes nor QuickTime plays FLAC natively but there are some software solutions available:
Or there are FOSS (Free and Open Source Software) alternatives which play FLAC natively, eg:
The difference between them is not in sound quality - they will all sound the same (now, there is a debate to be had around this statement - if you have a view about this issue, let us know) - so it's more down to what other features you want. VLC is very light on system resources and plays pretty much any codec natively. If, however, you are looking for a similar kind of front-end to iTunes, you might prefer the features offered on Songbird.
If you can offer DreamStreaming a report on your own investigations on this subject, or add to the debate through personal experience, please send the information to us and it could become the basis for a DreamStreaming information sheet.