Audio CDs are recorded in 16 bit, Stereo, and 44.1 KHz, the settings you should use to create the AIFF file. There are quality as well as speed differences between the different encoders, you can search out reviews on the various encoders to get an idea of their pros and cons. A couple of popular encoders for Macintosh computers are MPegger and SoundJam. Your encoder might ask you for settings, all of which you can adjust. The bitrate is how much information is flowing.
Less flow is smaller and faster, but, if it's too slow, quality suffers.
128 kbps is pretty standard, but for classical music a higher rate might sound better. Joint stereo tries to improve sound quality by combining similarities between the left and right channels, allowing more bandwidth for the music. Unless you have a reason for creating an MP2, you may as well stay with the default of MP3. However, if you want to save space or improve quality, you can try higher or lower bit rates, perhaps 160 kbps or 196 kbps for classical music. Try it and see how it works.