The story goes that H. Rider Haggard, having finished reading 'Treasure Island,' stated that he could do better and sat down to write 'King Solomon's Mines.' Did he do better?
Well, Haggard's plots and settings are certainly more inventive than those of Robert Louis Stevenson. It must be admitted that RLS could be a bit predictable. Do not look to him for much in the way of plot twists.
Where Stevenson outstrips Haggard and most other writers of adventure is in characterization. There is depth to those who people his stories, both the heroes and the villains and, in particular, those who are a bit of each (a la Long John Silver). Yes, his protagonists can be somewhat boring. They tend to be 'everyman,' junior edition, with all the failings of real human beings.
One might complain, however, that they do not do much deep thinking. Haggard is certainly more interested in bigger questions of philosophy, questions better served by the fantasy elements in his novels. But those who seek the answers lack the complexity of Stevenson's characters.
Let us face it, most people, most of the time, have their minds on the more mundane tasks of life, such as staying alive. So what if Jim Hawkins doesn't ponder the meaning of life? He can do that when he gets home safely.
Both were decent writers of adventure, and influenced those who followed. We would have no Edgar Rice Burroughs without an Haggard. Mr Hyde is an enduring concept, emulated widely.
I am certainly not going to pick one or the other as my favorite!