Since you're planning on using iTunes as your server to the Squeezebox, then Apple Lossless will be best since iTunes doesn't support FLAC natively. As long as you stick with a lossless format (either Apple Lossless or FLAC) you can convert from one to the other relatively painlessly down the road. (Look into an application called Max for the Mac that lets you do that conversion.)
The downside to Apple Lossless is that a Squeezebox is able to natively decode FLAC in hardware, thus reducing the burden on your laptop. Apple Lossless files need to be decoded on the computer, and then sent to the Squeezebox. FLAC also works on a wider variety of platforms. For instance, I use Slimserver on Linux with FLAC files and it works great. There is no iTunes for Linux, so FLAC works best for me in this situation.
I hope that helps.
Michael
The downside to Apple Lossless is that a Squeezebox is able to natively decode FLAC in hardware, thus reducing the burden on your laptop. Apple Lossless files need to be decoded on the computer, and then sent to the Squeezebox. FLAC also works on a wider variety of platforms. For instance, I use Slimserver on Linux with FLAC files and it works great. There is no iTunes for Linux, so FLAC works best for me in this situation.
I hope that helps.
Michael