How do you define "truly magnificent"? Is it about movement design (layout), finissage (decoration), in house construction (production capability), or something else? Depending on the answer, there are many choices. Here are some possibilities:
Vaucher 5400 series movements: nicely designed and laid out micro-rotor movement. Used in Hermes Slim de Hermes, Laine V38, Parmigiani. Can be finished to a very nice standard (Laine V38). Vaucher produces most of the movement content as well.
Any Lange you can afford. In particular, the original Sax-O-Mat (L921.2) is considered one of the great automatic movements. It can be found in the no date variant listed in the prior post.
Glashütte Original produces their own movements and finishes them nicely, although not as well as ALS. The 36-13 in the SeaQ Panorama Date is a very nice sports watch movement.
While I don't care for the use of the Villaret movement in the smaller Blancpain Fifty Fathoms models, the Caliber 1315 in the larger FF is a nice movement, finished to a quality standard.
Any Chopard L.U.C. movement is going to be well finished and well made. Here's an article that speaks to their workhorse micro-rotor movement:
https://subdial.co/blogs/news/how-ch...movements-ever
Parmigiani Fleurier makes well finished and well designed movements (they own Vaucher). The watches themselves until recently had a pretty quirky aesthetic and are not for everyone, but that makes them great values secondhand. The new models are getting a lot of attention and are hard to get.