mp3 vs ogg vorbis file size

I'm a recent convert to linux, and I have been looking into which file format is best to rip all my CD's into. I have repeatedly read that ogg vorbis has a smaller file size to quality ratio than mp3, so I decided to test it out. Using sound juicer and ripping to both formats I found my that each song ripped to ogg vorbis was 1-1.5 MB larger than its mp3 counterpart. Expecting this to correspond to a significantly, or at least noticeably better sound quality in vorbis, I listened to several songs from both formats and was unable to detect a difference. why are the files larger in ogg, when they are supposed to be smaller? is this related to using sound juicer, or is ogg actually supposed to be larger? do I just have bad ears to not detect ogg's better sound quality? I am very unfamiliar with music compression, so im not too sure where to start looking for answers.

any help would be much appreciated