is it better to rip files from a cd as a wav or aif file? is ripping to aif even possible?

Wave, because most encoders at least have wave file support. There are also no advantages to using AIFF over wave.

You can rip to AIF with CDex.

But, as Trelane said, it's not really worth.

Isen't AIFF the same as WAV, except the header within the file ? (AIFF header instead of WAV header)

Yes. And that's enough reason for most encoders out there refusing to encode AIFF streams.

Wave, AIF are all pretty much the same - what you want to do with the files determines why you would want them in that format.

If it is for best audio possible (better than any MPC, Ogg or Mp3 file), then look into Monkeys Audio or FLAC, they give exactly the same as the original CD, pretty much as Wave and AIF can, but they save a little on space and can have built in tags like artist etc.