> What is Windows Phone equivalent to Google Nexus series?

The closest equivalent to the Nexus series in the Windows Phone market would be the **Lumia** family, insofar that it's also (as of mid-2014) being produced by the same company that makes the OS - Microsoft. Luckily for you, it also offers the [largest selection of devices][1] of any Windows Phone manufacturer by a considerable margin, as well as (arguably) the best hardware. So in that respect you're spoiled for choice.

> devices receive updates directly from Google, without having to wait for manufacturers or carriers to push them to me

The **Windows Phone Preview for Developers** programme (in the process of being rebranded as Windows Insider) that you mentioned offers precisely that. By [signing up][2] you'll be able to receive new versions of the OS as soon as they're released, without having to wait after the carrier or manufacturer. The Preview programme is available for all Windows Phone devices (except those that originally shipped with Windows Phone 7).

In terms of longevity, pretty much all WP8 Lumia devices released so far (starting in September 2012 with the 820 and 920) either have already, or will soon, receive the latest version of Windows Phone 8.1, as well as the Lumia-specific firmware update named Denim. Also, most, if not all of these devices should be able to upgrade to Windows 10 when it's released later this year.

  [1]: http://www.microsoft.com/en-gb/mobile/phones/lumia
  [2]: http://dev.windows.com/en-us/develop/devpreview