I have owned all three and I think Tacs comments are right on the money; it's all about synergy. I disagree that the AI is definitely better; it all depends on what tickles your fancy sound wise.
Both the ARC and Counterpoint were used with Berning 2100, Moscode 600, BEL (original 50W class A), and PS Audio 200, the AI with Manley Reference 200's. The front end and speakers remained the same: VPI/ET, MGIIIA's.
To my ears the Counterpoint offered the most natural dynamics(very lively), and the most natural tonal colors; but I found it to have a funny "phasey" quality that kept me from enjoying listening whenever I wanted to indulge in "audiophile" aproved soundstaging. Beware! I found it very expensive to keep it in quality tubes. It's an all tube design and the three or four tubes in the power supply had to be of premium quality and fresh to sound best, as well as the signal tubes of course.
The AI had the best soundstaging by far, with very stable imaging; but I find it way too dark in a greyish kind of way, and it never really moved the way that it should. AI's have always sounded kind of slow and lifeless to me. Pretty hassle free tube wise.
The ARC is pretty natural tonally, a little on the lean side with very good imaging if not in the same league as the AI; but much better dynamics however.
Your system could probably use a less warm and corpulent sounding preamp to balance it tonally. If your listening is not done "in the sweet spot", my choice would be the Counterpoint. If it is, and you also want good tonal colors, the ARC would do it. If you value soundstaging and image stability above all else, the AI is the one; but IMO you would end up with sound that is too thick, dark and sluggish. All MHO.
Good luck and let us know what you decide.