I had two volumes of Spider-Man and one volume of Doctor Strange. I think there was a Fantastic Four and Cap one too.
There were three volumes of Spider-Man, sadly only two of Doctor Strange, two of Hulk, one Captain America and one Fantastic Four.
All were published by Pocket Books. There was also one Conan, but that one I never managed to get back then.
DC also had a similar series, yet in black and white, altered artwork and more random. Cheap too. They covered basically 60s stuff of Superboy, Superman, Batman... etc. . The Superboy was great in that it had Wally Wood artwork in it.
The Marvel stuff was superior and basically Masterworks in pb form... except for Cap... that was other stuff. In addition, Pocket Book also reprinted a number of random Marvel story arcs of their comics back in the early 80s. Star Wars stuff, Captain America's John Byrne drawn Baron Blood story arc... and others.
DC did the digests starting in roughly 1979 to about 1984 with Adventure Comics being the final stuff.