The only numbers I will ever spell are one and zero, and only when using them as a pronoun, or for emphasis, respectively.
Is there ever a reason to not to use symbols when dealing with numbers? Why would "fourteen whatevers" ever be preferable to "14 whatevers". It's just so much easier to read numbers as symbols, not spelled out.
(Caveat, not including multipliers, like "273 billion").
This kills me, but its not as bad as the habit of new articles/print authors to switch between first and last names of the same person within a few sentences.
They will introduce Jeff Snoms, and then refer to them has "Jeff" and "Snoms" interchangeably for no discernable reason. It gets really maddening when they are doing it with 3 or 4 people, so suddenly the story has 2x as many characters involved.
The German standard is to write out everything up to 12 and as English also doesn't say one-teen and two-teen that's how I always did it. (why not tenty-one btw? be consistent your numbers are all weird)
This is how I approach it. If there's only a few numbers mentioned and they're small, write them out. If there's many numbers mentioned, then they should all be numbers. And I catch myself messing it up all the time and going back to edit the one number I put in there because it just looks wrong. Context is everything, really.