I almost exclusively go with monsters, rather than Dark Lords. Nothing wrong with using Dark Lords. I just prefer using them very occasionally, because if you are always using them, it feels like the point of the setting becomes killing individual domain lords. Also, generally I like the feel of them as background figures. That said I have run modules where players contend with Strahd, Azlin, Mordenheim, Harkon Lukas, etc. I've also had this kind of confrontation come up without modules. I recall a player getting into it with Ivan Dilisyna back when Dorvnia was still a Domain (he was always one of my favorites because I interpreted as being heavily based on John Hurt's portrayal of Caligula). The player blew up the Dilisnya Estate with a combination of fireballs and science (as a GM I may have been overly generous in that moment). And remember running Castles Forlorn as well where Tristen ApBlanc comes up. I know others have also emerged in play. Also I tended to be more likely to use Dark Lords on Islands of Terror. So even only doing it occasionally over thirty+ years of play in the setting, many of the dark lords have come up. And often I had different groups. And if was a spontaneous campaign, I might run some of those modules as one shots. Most were long campaigns. I preferred Ravenloft, even in the black box era, as a main setting for me to run. But I would still say my percentage is probably something like 99% monsters, 1% Dark Lords (maybe 2 percent).
Also something important to consider, in Ravenloft, villains of all stripes usually function similar to Domain lords in that they were shaped through their own evil actions by the dark powers and the powers check system. So you don't need Dark Lords to have every adventure have the same level of villainy as a dark lords. As a setting it lends itself very well to pitting the players against unique monsters and villains laboring under strange curses. And you can make your own domain lords, and domain lords can exist in very very small areas, within an existing domain (the House of Lament for example).