HD Tracks sells files in a number of different bit depths and sampling rates. They range from 16-bit/44.1K (Red Book CD) to 24/192. The higher, the better, obviously. Though the quality of the original master definitely affects whether there is actually a noticeable difference in higher rates.
HD Tracks (the website, anyway) lists what rates you are about to download directly on the page...usually right above the playlist on the right hand side or above the description in the main window.
FLAC and ALAC are both losslessly compressed formats, so I'd stick to one of those for the best file tagging support (WAV doesn't support most tagging efforts...not sure about AIFF).