Definitely FLAC for audio because it's lossless, if you record from a high fidelity source....
exFAT for external hard drives and SD cards because both Windows and Mac can read and write to it as well as Linux. And you don't have the permission pain....
If you were to format the drive with extra and then copy something to it from Linux - if you try open it on another Linux machine (eg you distro hop after this event) it won't open the file because your aren't the owner.
Then you have to jump though hoops trying to make yourself the owner just so you can open your own file.
I learnt this the hard way so I just use exFAT and it all works.