IMO it boils down to personal preference. What does your ear tell you?
ARC makes the finest preamps in the world in many studied pro's opinion.
MAC has a warm, engaging "house sound" that has been carefully curated over decades.
Which music you listen to most and which speakers you drive are major factors in the sound signature you want.
While I am biased toward ARC I have heard some really magical MAC rigs. To be honest I'd like to add a MAC integrated driving a set of Maggie 1.7x to my small room system- even though my big rig is ARC pre-and power amp'd and it thrills me again and again.