Hi Polyfade-
The database we're using for GeoPosty is provided by Quova. Although your story about the accuracy comparison is intriguing, Quova's database ought to be the most accurate/dependable as it used for security and marketing by the likes of Facebook, Comcast, MLB and BBC. You can see more here: http://www.quova.com/who/
While you can get very close readings with opt-in html5 technology, I would not trust any database (including Quova's or Maxmind's) inside of 25 miles. If Maxmind somehow has better technology than Quova's, I would be interested to hear about it. Though, the comparison you are describing seems like it could be a bit of luck.
As you can imagine, I would recommend your sticking with GeoPosty. As developers, we will continue to invest our time in it. Currently on the horizon is a better system for filtering locations and a test portal so that wordpress admins can test their work (without traveling to India).
Quova, as always, is improving their data as they move forward as industry leaders.
Thanks and brgrds,
Matthew Pilon
GeoPosty Dev Team