My advice would be to use Apple Lossless, or AIFF for ripping. They use lossless compression which means, although the song is compressed, no data is thrown away in the process. In these formats, you can use software to simply convert to any other format if you need to in future, without having to re-rip.
WAV is essentially just ripping the CD as is - with no compression, it takes up a lot of space for not really any gain. It can also present issues for transporting data due to the way tagging works. For this reason, unless you have a very specific reason to use it, I'd avoid it.
Finally, unless you're incredibly tight for space, I'd avoid using AAC or MP3 - they use lossy compression which means data is thrown away during the ripping process - although this makes the files much smaller, this data can never be retrieved if you wanted to change to a different format. So if you rip everything to AAC now, then in a few years time decide you want to move to a lossless format, you'd have to re-rip your entire collection again. In my experience, this is really only something you ever want to have to do once!