Audio Research Reference Linestages

Yes- I have a Ref One, plus there are two local friends of mine who both find their Ref One's to be superior to any of the newer Ref series (except the Anniversary no doubt!)

Well, I have not owned any of the ARC Ref. series myself, but my friend has owned all four of them, (they skipped the ref. 4). I have heard his system countless times, and personally, I disagree with your assessment.

The One was always a bit noisy for my tastes.

The Two was slightly better, but not much.

(That being said, both the One and Two were quite musical, and possibly more so that the Three and Five that followed, but I would never have owned either.)

The Three was a big step up, IMHO. It was much quieter, and more transparent. I would consider owning this preamp.

The Five is basically just a better Three, IMHO. (Basically just more of the same, with slightly better dynamics and slightly better bass response.)
I recommend that you not bother with the Ref. Five, because if you dislike the Three, the Five will not be much better, (in my estimation anyway).

FYI, as you can tell, I highly prize deep, dark, black backgrounds, and the Ref. Three and Five preamps excel at that, versus the One and Two. (FYI, I own a solid state preamp myself, (Ayre K-1xe), primarily for that very reason.) Tube rushing noise bugs the heck out of me, and both the One and Two had it, albeit somewhat muted, but still, it was there. (I should point out that it never much bothered my friend, so perhaps I am just overly sensitive to it.)

My two cents worth.

ARC seems to have been on a course toward detail/resolution over the recent decade-ish. As a result, it does not surprise me that there will be some/many that prefer the earlier versions to the new versions. Personally, there are parts of the LS25I that I like better than the LS25II. I think this case is mostly having to do with the tubes used vs. major changes to the circuitry. These are personal issues or opinions and you are likely to get people strongly agreeing with you and those that strongly disagree with you. Neither is more right or wrong than the other - such comments are based on personal opinions.

Ref 1 is a an all tube 6922 based preamp.
Ref 2 is still all 6922 but with 6550C regulator
Ref 2 II is a hybrid with JFet input and 6H30.
Chassis may look similar but they are completely different animals.

I concur with Sutt's opinion.

Thank you for all answers and opinions.

Just to comment on a few things that I don't agree with.
My Ref One is dead silent. No tube noice at all.
But I had that problem with my Ref2 mk2.
Might be a problem with more sensitive loudspeakers, but until now it haven't been an issue for me.
Tubes at the moment are Telefunken E88CC and Ei E88CC which both are low on noice.

Yes, I assume that ARC always are aiming at more detail and higher resolution, but when comparing my Ref One with Ref3 I find Ref One to be better.
Higher resolution and more dynamics.
Simply more nerve and musicality.
But as you say, it's a matter of personal preference.