H'mmm. I'm not so daft as to have a favorite Heinlein book, but I still do like one post-1960 novel fairly well -- that being The Moon Is a Harsh Mistress -- and TEfL, bulging as it is with dreck, still contains some of his best writing (I refer to "The Tale of the Man Who Was Too Lazy to Fail" and to a lesser extent "The Tale of the Adopted Daughter," disturbingly perverse as the latter is). And Stranger is ... interesting. Not quite good, but interesting.

Donaldson will never make any top ten list of mine (not that I have any interest in creating one), but I think you underrate him. Yes, he is a would-be stylist who started out with a tin ear. He got rather better.