Aiff or Flac

AIFF better sound/larger files
FLAC more playback compatibility. 

FLAC is lossless compression format.  Music decoded from it is identical to AIFF.  The only difference is that listening to compressed file requires uncompressing on the fly, that can possibly affect timing of the samples coming out.  It could possibly make audible difference with some playback programs and interfaces like S/Pdif, but won't make any difference with async USB, Ethernet and WiFi.
I keep my music in ALAC, format similar to FLAC.  It saves me about 50% of disk space.   Take one great sounding piece of music and play it in both formats.  If you cannot hear any difference keep it in FLAC.  The only disadvantage of the FLAC is that some programs like Itunes won't play it.  You can always batch convert all CDs to different format, when needed.  I use XLD on the MAC for ripping, but recently fre:ac for batch converting.  It is great free public domain program for all platforms.  

https://www.freac.org/

When I ripped all my discs, I ripped some files to both FLAC and AIFF to compare. 

Granted, I compared with headphones on my Apple laptop computer, but there was additional background noise on all the FLAC files.

I determined that whatever additional computer resources that convert the FLAC files on the computer added additional noise.

I don't know if this would transfer over to decoding on audio equipment but I decided to rip to AIFF and avoid the possibility.

However, listening to FLAC files on Qobuz through my audio gear sounds great. I still wouldn't change my decision after my test, though. There's no gear that I own that can't play AIFF files. 

I use flac and everything sounds beautiful

I’m also a FLAC user. I compared FLAC rips directly to the original CDs before settling on FLAC for my music storage and was unable to tell a difference.

However, as someone else previously noted, while lossless, FLAC does involve file size compression in a manner similar to Zip files, though FLAC is specifically for music. FLAC assumes that your hardware is adequate for doing the decompression. Most modern equipment should be more than capable for this task but I suppose there might still be some gear out there that isn’t up to snuff.