Your best bet is to buy a large external hard drive and save the files in WAV format. Then you can convert them to any lossy compression format you choose (mp3, aac, wma, etc) and save them on a different drive. This way you can convert to a different format or use the same format with a higher bitrate, if you choose, without having to re-rip the cds.
That is what I do and I can tell you that it takes a long time to rip a substantial cd collection. I currently use mp3 at 192kbps. I wouldn't want to re-rip my collection if I decide I'd rather use mp3 at 256kbps or wma. I don't have to. I can just open the WAV and convert it to a new format.
If you don't have the disk space or feel you will be satisfied with just having the compressed formats, then spend a little time figuring out the 'best' format for you. A good compromise is mp3 at 192kbps. I've never been able to tell the diff between 192kbps and 256kbps mp3s. Mp3s are the most compatible with all playback software and portable devices, although newer formats may be slightly better.