John Truby, legendary Hollywood script doctor, utters this provocative quip: “What you choose to write about is far more important than any decision you make about how you write it.”
I’ve been chewing on this question. As someone most interested in writing “genre” fiction (as in fantasy and science fiction), I think his point is
An unpublished author has to wade through cynical editors and jaded readers; if he wants to get his book published and purchased, he has to convince them the investment will be worth it. If the author is trying to do that on the basis of high-quality writing alone, that’s very hard to do without the experience of actually reading it. But if the he has a unique and interesting subject about which to write, then he’s got a head start on getting people to read long enough to discern his quality.
The very best stories have both: an excellent subject that has draw of its own, and then a skilled author executes that story with artful prose and an elegant structure.
Consider the other cases: a story has a good idea but poor execution. The better the idea, the more I’m willing to put up with bad execution (Chronicles of Riddick). If I have a dumb idea, I don’t care how well it’s done, I can’t force myself to slog through it for the sake of the artistic beauty (Twilight).
Here’s my operating principle I’m getting from all this: do both well, but realize that a great subject buys you time for every other art of fiction. Make sure your idea sizzles before refining the recipe.