I let the boys, 6 and 9, watch the Trilogy over a long winter weekend and they are still runnin around mock shooting each other. I refer them as the "Eastwoods" when they have been after it!
They also liked "Two Mules for Sister Sara"..another one I didn't see mentioned.
I'll sit thru any CE film, even the gooey ones..
Quite a list on Wikipedia.
Back on subject. I can't pick just one, I like 'em all!