Both AIFF and WAV files are the same as far as quality is concerned. Both are fully uncompressed audio. A four minute song can rack up about 40+MB of space. AIFF format is more compatible if you're strictly speaking Mac. WAV files can not be used for some system purposes while AIFF can. Under normal circumstances it's nothing to worry about though. If you're planning on using the files on a PC or on the internet WAV is more compatible as some older PC's or PC apps won't accept AIFF where as a Mac will accept playback of both formats.
If your audio software doesn't support AIFF format then you can use Audio Converter Plus to convert AIFF to WAV without quality loss.
Run the downloaded file audioconverter.exe to start installation, which is fast and requires no knowledge. After installation, double click on the new icon, you will see the user interface below.
Add the AIFF audio files from the "File" menu in batches. You can add few files at once or entire folder with AIFF files. Audio Converter Plus can scan all subdirectories if you wish.
At the right bottom field you can see an Output Folder option. Click the "Browse" button to set an output path, which will be the destination folder of converted WAV files.
Select WAV encoder from dropdown list and click the "Encoder options". Use the "Same as original" choices to keep original audio format. Please note that output WAV files may takes all free space on your hard drive!
Click the orange "Convert" button, the conversion task will be started immediately.