Peter Cushing is the only actor whom I have seen that I would rank as an equal if not a superior to Christopher Lee. Not only have Cushing Lee worked together in pefect sync in multiple films, Cushing has been able to hold his own in worse-than-second-rate movies involving ridiculous plot lines, disgusting special effects, and horrible supporting casts.
One example in which I have seen all of these three awful elements molded into one film (out of the approximate ninety movies involving Mr. Cushing, I have seen twenty of them in my so far short existence of fourteen years) was Island of Terror. (I swear the goo coming out of the turtle/vacuum-cleaner "monsters" was congealed oat-meal.) This movie would be dubbed on a personal level as one only required to complete a collection of Cushing movies. He is really the only good actor in the film, providing a serious yet slightly comedic performance that was highly impressive.
One of the few reasons I feel Vincent Price is far more widely known than Mr. Cushing is that he was in better-made movies. Cushing fans will agree that he was one of the best actors of his time and of times yet to come.
In an afterthought, a reply to the original thread of what is my favorite Cushing film without Mr. Lee would probably have to be either The Revenge of Frankenstein or Frankenstein must be Destroyed. These are two very powerful performances of the good Baron. Yet, this may or may not be an accurate decision due to the fact that I have seen but twenty movies with him in it.