Harbeth vs Vandersteen vs Sonner

Never heard Sonner, but as @twoleftears mentioned, Harbeth and Vandersteen are very different animals.  Harbeth will generally sound more rich and midrange centric where Vandersteen will sound more detailed — some will say more “neutral” — with superior 3D soundstage capabilities.  Structurally their designs are very different in that Vandersteen uses first-order crossovers and time-aligned drivers with fairly inert cabinets whereas Harbeth uses none of those things.  In short, both are excellent speakers but if you love the strengths of one you’ll probably find the other less appealing. 

If none of this means much to you, your best bet is to get out and listen to as many different speaker types as you can (and there are many) with your music so you can drill down on what characteristics and designs are most appealing to you.  Listening preferences are as individual as fingerprints, so you’re the only one who can identify what they are.  So go have fun listening whenever you can do so safely.  Hope this helps at least somewhat. 

I am a Vandy fan, as most here know.
I haven't heard of Sonner, but their website looks impressive and speakers appear to be well constructed.
My concern with Sonner is the 3.8 minimum impedance they list for the speaker. That is pretty low, so I would think you would need an amp with some 'muscle' to allow them to perform at their best.
It looks like Adirondack Audio in Brooklyn sells them.
I might just call for an audition.
Bob

Speakers are like running shoes (all shoes for that matter, as well as skis and bikes and books and many things). If there was such a thing as "the best running shoe," every Olympic athlete in the world would wear them. But there isn't, so they don't. The best shoe is the one that best fits your foot, that you feel most comfortable in, that allows you to run the fastest in your price range. Your best shoe is not my best shoe anymore than your feet are shaped like my feet.

Or ears. You have to try them all on. Listen. Decide which sounds (fits) best for you. None of our opinions should have any bearing on your personal preference.

After a few drinks, I have taken to call my Treo.... Cleo... ha no worries, I have heard two of the three ( not the Sonner ) and they provide vastly different but alluring soundscapes... while I prefer the Treo as others wisely said, you may not.
aint it grand to have choices!!!!!

vandy and harbeth longtime respected speakers, for accurate, musical, coherent sound

sonnet?  never heard of them... but new stuff can be good too, sometimes...