I have raspberry pis b+, 2 and 3. Also an ODROID C2.
I’d like to know which one is the best as an end point with ROON Bridge into an AudioLab Q-DAC
Cheers
Shouldn’t matter, they all do the same job. I use C2’s as endpoints. Find them very reliable.
I’m sure all usb outputs are the same but sometimes I read people saying you need a clean feed like using the ifi or a usb with no power just data.
Do you use the stock PSU? is it for your main system?
Yip, I use the stock PSU. It’s running Arch Linux for Arm and it’s my transport/endpoint for my main system, USB out to Schiit Yggdrasil into ATC preamp and active loudspeakers in a treated room. Roon Server is running elsewhere in the house and connected to C2 via Ethernet through 3 unmanaged switches.
brilliant
sounds like the C2 will be my endpoint for the main listening room.
One thing to note - there’s no Armv8 build of Roon Bridge yet, so you have to run it in a Armv7 chroot for the time being, otherwise a C1+ will do the job.
Nonono… Choose the Pi, choose the Pi. 
Seriously: when connecting a USB DAC, the Odroid will probably serve you better.
One of my Pi’s is connected to a linear PSU, though I’m not sure if it matters a bit – or at all. As for your USB cable: I prefer blue, but your preference may differ.
I use a BeagleBone Black. Works flawlessly. And doesn’t have the bus problems the Pi does.
It’s not one of the ones that OP listed, but the title of this thread asks the more general question, “Which ARM computer?”
To that I’d reply that you can’t go wrong with a Cubox-i. Sonicore chose them for their first Roon Endpoint for a reason.