Just my experience with various MP3 players, PowerBook, iMac, PC, etc. --
224kbps AAC is about equivalent to 320kbps MP3. I don't notice too much of a difference between 224 AAC and 256, but below 224 is noticeably not as pleasant as 320 MP3...YMMV depending on your sources, amps, and cans.
AAC is an MP4 codec, and ALAC is probably based on similar coding, but AAC is lossy, so bits of information are discarded just like MP3, while ALAC is bit-for-bit perfect and compressed without any loss of data just like WMA Lossless and FLAC.
Apple losseless (ALAC) uses the .m4a extension, but it is different from AAC, which is lossy and also uses the .m4a extension. They share the same extension but are entirely different, which actually casues problems in some cases (like when your adding everything to foobar, which can't play ALAC but can play AAC.