The best story (albeit still in progress) that I've read is
French Whines by an author not on this site (I believe, at least!) called CS Fox. It pushes all the right buttons for my particular version of the AB/DL Fetish, and effectively conveys a crushing mood of psychological helplessness whilst still revealing sparkling touches. Above that, it's pretty well written- grammatically sound and has sufficiently likeable or hateable characters. Several other of his stories (on the same site) are also pretty enjoyable. Although the site is predominantly furry, they do have some non-fur related AB/DL stories (such as this particular story of "French Whines"!)
On this site, I very much enjoyed reading teddy564339's
Cody and the Baby Start-Over Program. Again, I enjoyed the development of character and relation over time- and I am a fan of the whole "diaper institution" concept.
Finally, covering the more DL-orientated aspect of the fetish (ie closer to erotic fiction), I very much enjoyed with about a Sorority Initiation, in which (in tandem with a nearby Fraternity) the main character meets her future husband, through various humiliations. Despite being fairly indulgent in its purpose, again the grammar, structure and style were good enough to be engaging rather than distracting. Unfortunately, it appears half the stories that were on Daily Diapers' list (where I first read this) have disappeared, so I can't give an exact title or name the author. If anyone wants to go and look for it themselves, I must warn you, it's fairly rauchy!