Best content generator is the one you write yourself, because then you are the only one who is using it. My current generator has 56 million sentence fragments that I can then fuck around with. Most content generators have heavy footprints so as soon as lots of people start using them, they lose a lot of value.
If you want an off the shelf product or basically readable text then you're looking at The Best Spinner and products like it, but they have obvious limitations and there's a lot more time and hassle involved in spinning than in just letting your text generator run wild.