(first time poster)
I'll try to keep this short... Audacity uses the freeware LAME encoder, which is known to produce so many of those poor early MP3 files. iTunes uses the commercial Fraunhofer encoder, which IMHO produces far superior results. And since Apple paid to license the Fraunhofer encoder for you, it's the only legal way I know to have it unless you pay for another commercial program like Adobe Audition (very expensive!)
I've used both PCs and Macs in music production, and I always encode the final MP3s using a Fraunhofer encoder. I'm not a huge fan of iTunes, but it definitely gets the job done, and for free. Just remember to set the Import Settings to MP3 Encoder. I typically set most of my recordings to 128k stereo, no VBR, 44.1 kHz sample rate, joint stereo, and I always check to use error correction whether the disc needed it or not. It doesn't slow most new drives down too much. Oh, and I also check the Smart Encoding Adjustments and Filter Frequencies Below 10 Hz (20 Hz is the lowest the human ear is supposed to be able to hear, so why have the extra noise in there?)
Try ripping one track. If you don't like the results, set it to 192k and rip again, but above that and I don't think you're getting much value out of the increased data size. I know people swear by 320k, but I've made my MP3s with Fraunhofer's encoder at 128k since 1996 (starting with Cool Edit '96, which eventually became Adobe Audition) and have rarely needed to set the bitrate any higher.
Hope that helps, and happy ripping!