Unfortunately, your question is dependent upon the listener's ears.
For me, the answer is Vandersteen.
I've owned 3 Proac models and subsequently 3 Harbeth models over a period of about 30yrs.
I've owned ATC for the last couple of years.
While they have all been fine speakers, I've found ATC to offer superior timing, dynamics and broadband neutrality built around engaging and realistic mids.
For me ATC are the more flexible, in the sense of sounding confident and convincing with any type or genre of music - classical/jazz/rock/electronic etc - which suits my eclectic music tastes.
+1 for Vandersteen. I owned Harbeth speakers for years, various versions of the SHL5 and the model 40. I also had Proac Response 3's. For me the Vandersteen's do everything the Harbeth's and Proacs do well and build upon those strengths. My advice too you would be to go listen to any of the speakers recommended in this thread. Your opinion is the only one that counts. Good Luck!
Hard to go out and listen to these days. And I am not in a hurry, just thinking that I might want to go in this direction soon enough.
Vandersteen is very popular, and I am sure for good reasons.
ATC is interesting. Active or passive ? Which models ?
Verity and Reynaud..why not?
Rockport - too expensive.
Any of those can work equally well with both SS and tube amps ?
It is a common wisdom that Harbeth need SS and ProAc are better, generally speaking, with tubes.
ATC would need a lot of SS power, unless already powered, correct ?
" It is a common wisdom that Harbeth need SS and ProAc are better, generally speaking, with tubes." Says Who?
Harbeths are designed to present an ‘easy’ electrical load to the amplifier and will work well with valve (tube), solid-state and digital amplifiers. Playing loudly in a large acoustically dry, well-furnished room will demand a powerful amp. Conversely in a smaller setting listening closer to the speakers, much less power will be needed.
I currently own 2 ATC models, the passive stand mount SCM19 and big(ish) SCM100 active towers.
The 19's require a decent amount of power, 120 -150W, and quality SS would be best IMO to exploit their superior dynamics and bass tautness. The 19's replaced my Harbeth M30.1's.
Ultimately, active is the way to go with ATC and I love my SCM100aslt's - but if you already own a suitable amp the passives are still great.
Which model depends on how much you're prepared to spend and what your room will accomodate.
Definitely worth a listen to see if the ATC sound appeals.