iphone song import formatting?

generally, the encoding format does not make that much difference in file size. however what does make a large difference is the bit-rate, and type of bit-rate encoding you use.

the lower the bit-rate, the smaller the size, but the lower the quality of the resultant file and the reverse is generally held to be true, the higher the bit-rate, the better the resulting file sound quality.

Variable Bit Rate (VBR) - if you choose custom under the Encoder settings (Advanced/Importing/Settings) then the encoder varies the bit-rate in the resulting file dependent on what is happening within the song to try and keep the fidelity of the track as true as possible, but to also save on file size where it knows it can (during quiet periods etc).

http://www.mp3-converter.com/mp3codec/bitrates.htm