ARC LS1, LS2, LS3 , or LS7, which to buy?

Viridian, I have used an LS2B from 1992 to Jan 2006. Into an Aragon 4004 Mk. 2 via RCA until 1998, then into Rowland 7M monoblocks via XLR. LS2B has always performed flawlessly without a single glitch. Lots of gain. . . Could only turn the volume up max 2/5 of the way. Great soundstage; slightly warm sounding; very pleasing, perhaps without the super detail and extremely extended top you can expect in the newest designs. it contains a single 6922 tube. I never experimented with premium or NOS tubes, but only used stock tubes supplied by ARC. I suspect that a good Amperex 7308 or perhaps a 6H23 would do wonders for this unit. I still own mine. One of these days I'll do some experiments with fancy tubes. Sorry I do not have any info about the other fine ARC models in your wishlist.

Marty, John is absolutely correct about the balanced design of the LS2B being half baked. The device has XLR and RCA outputs, but only RCA inputs. The XLR outputs are using some kind of technical alamagoosa to fake the balanced signal. . . . and regardless whether its sound were 'pleasing' or not, it does lack the phonostage you are seeking.
I have replaced my LS2B January last with an ARC Ref 3.
I have had only experience with the 4004 Mk. 2 in the Mondial lineup. While it is a competent unit, better than the Bedini, Hafler and PS Audio I had the opportunity of auditioning at that time, it is fuzzy and unmusical, when you compare it to top ranking brands of the same period. If you were looking for a solid state amp of the mid to late 80s vintage, I would suggest 1st or 2nd generation Rowland monoblocks. price point will not be staggeringly higher than Aragon 4004, but you would find yourself musically in a different world all together.

JAFOX, is your experience with both the original LS2 and with the later LS2B? I can definitely fault my LS2B for lacking top-2-bottom extension, harmonic definition, and for sounding relatively hazy, but not really for lack of staging. Furthermore, I confirm I find the sound of my LS2B to be somewhat warmish, with a moderate bloom in the midrange, rather than dry. Is it a case of the two of us hearing/judging thing differently, or could unstated design variability on the same product version account for some of our differing perception?