Best to read everything and figure out what you like.That hasn't really changed much.
During the course of my four semesters of Short Story Workshop at a local junior college, I had an ongoing friendly debate with the professor in which I asserted that (1) all fiction is genre fiction, because all fiction has a genre, even if the genre is "contemporary realism" or "historical realism," and (2) the distinction between "popular fiction" and "literary fiction" is completely artificial, because there is very little fiction that wasn't intended to be popular.
A lot of books considered classics these days were serialized stories that were highly commercial. Think Dickens. I can best compare Dumas to James Patterson today. Only Patterson seems better with his money matters.
If you want to dig deeper into this, check out the book Jane Austen's Bookshelf. It deals with how critics selected what we now considered classics by women authors from the 19th century. It's pretty fascinating. Though the writer inserts themselves a bit more than I would like.
