Best HiRes/lossless format and why?

There's a lot of information out there already.

I chose AIFF because it's uncompressed. While ALAC, WAV, and AIFF are all 'lossless' formats, I figure there's less system overhead when it doesn't have to decompress ALAC. If I have a special album, I rip to WAV, but one loses artwork and tags when doing so.

Use XLD for your rips. Much better and more flexible than iTunes rip.

FWIW, I'm running a Mac Mojo Mini server, external 4TB hdd, powered by the Mojo Joule III power supply. Those changes made a HUGE difference over a stock Mini.

One option is to remove timing by using networking. It will make computer and playback program (or format) irrelevant. It doesn't even matter that I use computer for other things (it is my main computer) at the same time. Timing is recreated on the other side of the network bridge. I use wireless transfer that keeps my computer away from the system. Money spent on special computer mods, power supplies, playback programs can be used to reduce jitter using good reclocker.

To my ears, AIF has a *bit* more high-frequency emphasis than FLAC, but the bass on AIF is more transparent, so I lean towards AIF for the more realistic sound.