Which one, AAC,AIFF,MP3,WAV or Apple lossless??

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!

Just to clarify. AIFF doesn't compress at all. It's just Applespeak for standard uncompressed PCM, and takes up the same amount of space as WAV.

Ah, nice one Andrew. Apple Lossless it is.

Rip to AIFF/WAV (it's the same thing in essence) and you have  the best available quality from your CD rip (it's not downloading, it's ripping). Then if you want to save space on your iDevice, select 'export higher bitrate files at 256kbps' in the relevant iTunes menu.

Most of my music has been downloaded to AAC some on Lossless. Now I have noticed that I can change a AAC song to Lossless when I right click is this any good?

No, it's a waste of time, you'll just use more disk space with no increase in quality.

Use Apple lossless. The file sizes are slightly smaller than AIFF and WAV which is always a good thing, and no data is thrown away during compression. As for converting from any lossy compression (like MP3 or AAC) to lossless or uncompressed (WAV, FLAC or Apple Lossless), there is no benefit most of the time because it can't put back what has been already thrown away.

Thank you for your help its a little clearer now

No, always, always, ALWAYS rip to WAV, then once you have that file, you can convert it to something else,

everything plays WAV and hard drive space is so cheap now, unless you really are a "tag sleeve-art tart" there is no

reason not to use WAV

Unless of course you want to see album art, track titles and so on, in which case FLAC or ALAC are preferable, as they carry the tags. And anyway, if you rip in FLAC or ALAC, you can always uncompress (decompress?) to WAV or AIFF later if you wish – they're lossless, after all.

For use on an iPod, I'd stick to ALAC (aka Apple Lossless).

What Andrew said. I'd never rip straight to WAV unless, as someone else said, I had a very good, specific reason to do so (and I can't even think of an example of such a reason).

EDIT I'm not sure if you use an Apple machine or a Windows one. If the latter, WMA Lossless is an option.

As Andrew said, rip to alac if iTunes is your main player (you can always decompress later if needed) and you also listen to the music on your main system (you probably don't of course, as you're ripping CDs for portable use). I then think 320 or maybe 256 kbps aac is fine for an iPod, you won't hear the difference from alac, the files are half the size and the processor has less to do. If that makes you itchy, then stick with alac for your iPod too.