Hi Mick,
I cannot really point you in one way or the other on these two choices. I would recommend that you listen if you can, obviously the LS-26 is your best opportunity there. The reason being that the LS-5 was based on the 6922 tube, which has many substitutions. The Ref 2 mk II and the LS-26 ar based on the 6H30 tube, which really have no substitution. So the haze that you found on the LS-5 could be related to the 6922 tubes (age, poor quality, etc). The LS-5 mk II/III have a great reputation to be sure, but tube choices are so important here. E-mail Audiogon member Jafox offline if you need more info here.
All of that being said, if it were me, I would probably go with the ARC Ref 2 mk II because of the tube power supply. As a 30 year 'audionut', and a owner of the ARC Ref 3, I firmly believe that the tubes in the power supply are just as important to attaining the 'tube sound' as the tubes in the output stage. Also, if it did not work for whatever reason, I could re-coup more of my investment on the Ref 2 mk II than a LS-26.
Happy hunting,
John
PS: The word 'hazy' absolutely cannot be connected to the Ref 3. I have a feeling that your friend's LS-5 may have had tube issues.