The principal reason I'd probably select a Primaluna over the ARC is that with the ARC is what you hear is what you get. You really can't change the tone by rolling tubes. With the Primaluna you can change the tone quite effectively by simply changing tubes. The ARC output impedance will be an easier load for many amps. This might be a problem for some Primaluna users. It was so for me on an earlier Primaluna pre.
There are other issues which would probably push me toward the Prologue as well but for me those are the relevant ones, and frankly if I were to buy one now I would probably not buy either.
There are other issues which would probably push me toward the Prologue as well but for me those are the relevant ones, and frankly if I were to buy one now I would probably not buy either.