If you're about to re-rip your entire library, rip to FLAC!!! I cannot stress this enough. From FLAC, you can create anything you need, whether it is ALAC, AAC, MP3, whatever. Now that I finished re-ripping my entire library, I have a box full of CD's that I'll probably stick in a closet. Unfortunately, I have also acquired about 30 - 40 CD's in digital format from Amazon. These are in MP3 VBR format. (good quality, but not lossless) I am now in the process of deciding which of those I really love enough to re-purchase in CD format.
Rip once, rip right!