What is the highest quality audio format offered by iTunes?

What is the highest quality audio format offered by iTunes? I'm a lifelong pc user who has made the switch to iMac. FLAC was my audio format of choice. When I attempted to transfer all my pc information stored on a Western Digital external harddrive to my new iMac, only a portion (approximately half) of my music files transferred properly. The rest is randomly splattered around without any organizational identification. I'm assuming I'll have to delete those files and then enter those files into iTunes and want to transfer in the highest quality audio format offered in iTunes as possible. Live Apple Support attempted to help me download two programs that I used on my pc with downloading music files (EAC - Exact Audio Copy) and copying those files to blank disc (Winamp). I would prefer to use those programs on the new iMac if possible. If this isn't possible because of incapability, then will iTunes provide the same audio quality I had with my my pc?