What an interesting question. I own a pair of Harbeth M30s, which I brought in to replace Vandersteen 3a sigs (which had replaced 2ce sigs). There was no contest. I listen to a lot of classical music, and the sound of strings (massed or otherwise) on the Harbeths was richer and more fleshed out than the Vandersteens...so much so that certain CDs I considered almost unlistenable on the Vandersteens were suddenly listenable on the Harbeths. I auditioned a few other speakers in high end shops both before and after getting Harbeths, none of which struck me as being as pleasant as the Harbeths, with one semi-exception (though the electronics were not the same as mine of course, so one could argue that the comparison was flawed). I listened to Wilson Sophias (which didn't impress me much at all in 2 different set-ups), a Wilson-Benesch something-or-other, some Revels, some ProAcs (D28? I think, which were interesting--I could have spent more time with them), Sonus Faber Cremonas (which had a very interesting mid-range, but the tweeters had a bit too much "tizz" in them), some mid-priced Dalis (blah), some little Sonus Fabers (Cremona Auditors?--too much "tizz" in the highs), those wierd looking German speakers (MBL? -- I couldn't get out of the room fast enough), Audio Physic Scorpios (which I kind of liked, though not because of fabulous mids)...and I can't remember what else.
The "semi-exception" to the list was the Avalon Ascendants because of everything else they do well, but I'm not sure their mid-range is exactly better than the Harbeths. The overall sound seems notably more transparent and holographic, and I'm a sucker for that, and, after some agonizing, decided to buy the Avalons. However, I'm not selling the Harbeths. As one dealer buddy of mine from way back said to me recently, "Harbeths are for when you're tired of everything else." (And he's not a Harbeth dealer.) I can really see where he's coming from.