iPod AAC, MP3, Apple Lossless?

It all depends. 320kb AAC and Lossless are pretty close and depending on your gear you shouldn't hear much of a difference if at all.
On my dad's stereo B&W 802s, etc. I do hear a difference to Lossless but none between Lossless and CD.
If you hear it and have the space go Lossless, if not 320 AAC should be sufficient, maybe even less depending on your stereo.

I rip everything in Lossless and 320 AAC. Lossless for the home stereo and beter headphones and 320 AAC for on-the-go and my iPod.

ALAC (Apple Lossless) is perfect for archiving as you retain every piece of information on the original audio CD while the ALAC files take up only a bit more than half the space of the original files on the source CD.

As for the iPod library, FWIW I have found that 192-VBR AAC is as hi-fi as the iPod (mine is a 5.5G with Shure E4Cs) can reproduce, and higher bitrates do drain the battery faster.

Apple Lossless is, of course, the best.

But, unless you want to use the CD rips for backup/archiving and have them just for listening, just go with whatever format that best suits your needs: If you have plenty of space go with high bitrate aacs (192 or maybe 224, 256 or 320) but if you're pressed for space (like I'm constantly am on my MacBook) then 128 actually is IMO the sweet spot between sound quality and file size.

I rip all my CDs as aac@128 (or even aac@96vbr for certain things) and use an AirPort Express and AirTunes to connect my MacBook to my Onkyo receiver (or I use my 2G nano when I'm not home, where the low bitrates even helps the battery last longer), and for one who grew up with LPs and mixed tapes during the 80s, the quality is - for the most part - more than good enough.

A note at the end: There has been more than a few threads on this topic, so maybe a search/browse is in order for your next question...

I think it comes down to this:

If you have a 1 GB capacity Shuffle or a nano, it's probably best to go with 192 kbps data rate AAC or MP3 format to keep flash memory usage reasonable.

If you have a 5G/5.5G iPod with hard disk storage, you could go with 256 to 320 kbps data rate AAC or MP3 format, especially if you use a high-quality portable headphone like the Shure E3c or better model.

AAC does a very good job. Frequently the only way you can pick up a difference is because it doesn't render frequencies above a certain level, but that level is often not in the hearing range of many people. In terms of sound quality of the frequencies that all such codecs can render, high bitrates are indistinguishable from Lossless much of the time.

I use Lossless as it's a good archival / transcoding source. But a sizeable portion of my library is also high-bitrate compressed. Honestly, if I specifically want to listening to something in the living room where I have the megabuck rig, I dig out the (SA)CD. But for most purposes I'm pretty happy listening to high-bitrate compressed.

I'm now back to running brute-force on the fly transcodes to my MP3 players from Lossless data on a quad-core using the fastest acceptable MP3 encoder @ 160K. In many situations it can be faster than transferring a Lossless audio file. My player runs for longer, I'm not giving up much quality vs portability and I can put more stuff in.