You want me to talk about what? Quirk versus mainstream? My darlings, I'm a Word Whore and not just any Word Whore. I am the Word Whore who thinks explosions are plot points. Who am I to address writing a mainstream success? It isn't as if I've penned a flock of them. In fact, it's entirely possible I wouldn't know mainstream if it jumped up and whispered an indecent proposal in my ear.
I go so far as to posit that few people know mainstream literature until a book becomes mainstream literature. Which is to say, popular.
At one point, it was Oprah's book club that made a story mainstream. But unless your tale was a major downer guaranteed to send readers dashing for the Prozac, you stood no chance whatsoever. These days, publishers will tell you they're looking for 'the next ________' - you fill in the blank with the bestseller du jour. Harry Potter. 50 Shades of Gray. Twilight. At least tragedy isn't necessarily the prerequisite for mainstream these days.
That said, do you see the problem? Any story following in the footsteps of someone else's is a day late and a dollar short. The wave has already crested. This isn't to say that some authors haven't made a pretty penny writing stories in the vein of whichever bestseller speaks to them. A few have. But I can't name more than one.
As for quirk? Define Harry Potter. Or 50 Shades of Gray for that matter. Twilight had enough quirk that it enraged an entire cross section of vampire fandom. Not bad for a day's work.
Point being, I suggest that quirkiness leads to mainstream success. If shoveling the same old story out the door day after day didn't lead to rapidly diminishing returns for publishing houses, they'd do just that. It is about the all mighty dollar after all, yes? But, alas for publishing's bottom line, readers are so fickle! Jaded book sluts, even, always seeking something new to sate their wicked appetites. Yet at the same time, those readers desire the strangely welcoming and familiar - as if by falling into a new story, the reader had come home to something they'd never seen before. When that happens, new love kindles the light in a reader's heart. That is the stuff that runs a story right up the sales lists, for readers, once in love with a book, DO kiss and tell.
Too quirky? I'm sorry. Was someone just implying that it was possible to be any quirkier than Platform 9 and 3/4? Or Nearly Headless Nick? In fact, it is entirely possible that JK Rowling has taken out a patent on quirk. It is clearly not an impediment to getting sucked into the mainstream.
Now. The difference between literature and genre? Easy. Wagner (opera) is literature. Bugs Bunny is genre. As to which is preferable? Who's singing Wagner in your head right now? Elmer Fudd? "Kill the wabbit, kill the wabbit . . ." Or anyone else on earth who didn't come from an animation cell?