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.
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.