Hi ALG,

If this is strictly car listening, lossless isn't so critical. But, I always rip my CD's to lossless and generally I don't convert when I load my Ipod (which I plug into my car).

Lossless is best. From your list only WMA offers that capability.

MP3 and AAC? AAC is considered to be the better format. BUT, it really is more strongly influence by bitrate. Lots of downloads are 128 kbps (kilo bits per second, per second making this a rate, or speed value). The more data you are moving per second the better quality the file. I find 128kbps to be too noticeably inferior. In my car experiences, 192kbps is the threshold where quality difference are almost no longer noticed. 256 is a nice default value. At 256kbps, files are still small but quality is nearly as good as lossless. Many may notice its short comings in a good listening environment. 320kbps, is very good quality but the size is so big you might as well do lossless.

I don't use WMP, and haven't since I use Mac's. I use iTunes but, at least on the Mac platform, you can't use iTunes to load a flash drive. iTunes only interfaces with iPods for file managment.

You can use a flash drive as you iTunes library and get a 3rd party script to manage multiple libraries, so in truth you could use iTunes with a flash drive if you were highly motivated. You have better options though already.