This is a tricky one. I believe that the house with the greatest consistency in style (from tha ones that I have tried of course) is probably L' Artisan Parfumeur. I have found several fragrances from this house that I like but the more I try the less I feel like actually owning a bottle. There is an opressive underlying accord in every scent and somewhere along their progression one tends to smell different bits and pieces from different other scents of the house. Duchaufour's creations for Eau d' Italie on the other hand share a common style but not a specific accord.
Serge Lutens on the other hand is quite consistent in style but the core of the consistency is taking several ideas ti their extremes. The sweet spice accord is their in most fragrances but the ones that I consider more impressive are the ones that break from this rule (Borneo, VO, Sarassins, ISM, Tubereuse Criminele).
To wrap this up, I like consistency in ideas but consistency in use of materials is really boring and sort of drags the entire line in a level of interest which is lower than the level of interest of each individual fragrance.