FLAC is lossless so it will be the same quality as the audio on the disc that you are ripping, which will be the best quality possible from that disc. However, music CDs contain 16-bit audio as higher bit depths take up much more room on the disc and the added quality is not noticeable for most people.
Audio DVDs are 24-bit and I think some Super Audio CDs are as well but neither ever became very popular. The files that you can buy on sites like HDTracks don't even go up to 32-bits.