Yeah, the subject comes up periodically. And the answers are as varied as the kinds of music people enjoy playing, and the way they play -- Chord Melody, Fingerdancing, or Noter & Drone.
I, for example, am a hardcore Noter & Drone player of 15th century to 19th century Anglo-Scottish Border Ballads and their descendants as played in this country. I want a dulcimer not more than about 6" wide, not more than 1-1/4" or so deep, with a 1" tall fretboard, staple frets, and Just Intonation. Those traditional instruments have what I call a "high silvery" sound. John Knopf, Bobby Ratliff, Dan Cox and Kevin Messenger all make dulcimers of that Traditional type which I would be proud and happy to own. And I do own dulcimers by John and Bobby.
The kind of dulcimer I prefer has changed wildly over the last 40 years. Originally I liked, and built, deep, wide dulcimers with much more baritone/bass response.