Castle films have a better reputation for picture quality than Universal 8. According to Scott MacGillivray's book, Castle rarely worked from anything other than 35mm fine grain master material. U-8, in an effort to get a large number of titles on the market in a hurry, used 16mm master material, sometimes even "duping" portions of Castle release prints.
Their editing was also sometimes sloppy; their version of Hitchcock's "Frenzy" actually omitted the scene in which the detective discovers the clue that "cracks" the case (I had to splice it in from a Castle print or the U-8 digest made no sense!)