Do you find that the stories that come easily to you are your better ones? Or are the ones you agonize over a higher quality? Or do you think the hard ones are better but you get more feedback on the easy ones?

Generally speaking, the ones that pour out of me are better written, in terms of style/loveliness of prose, and oftentimes in characterization, but the agonizing ones are the ones where the plot works and everything ties together in the end.

I think a combination of the two approaches works best in longer stories...

Actually, I've only ever written longer stories with that first burst of inspiration and then long agonizing stretches of two or three words at a time, so maybe I'm not the best judge...