The German site “Die bemerkenswerte Karte” (The Remarkable Map) by the German Cartographic Society (DGfK) reports about OpenMapSurfer.uni-hd.de as a remarkable OSM base map, because of it’s unique combination of high information density on the one hand and appealing aesthetics on the other hand. In particular the high quality automated label placement algorithms implemented in OpenMapSurfer contribute to this.
Judge yourself.
more info on OpenMapSurfer and the relevant scientific publications.