A Kindle from AMAZON is based on Android Opensource Code but is totally open to AMAZON to search your habits.
Google Android is searched by Google, who makes no bones about it and Serge Brin has warned everybody for years that "There is no privacy on the Web, everything you do is monitored while going through the government controlled nodes."
But, to date, Google has never tried to take over somebody's device -- the worst they have ever done was to uninstall an application that was in their PlayStore that was found to be a malware. Lots of notice was given on this and if the user wanted it they could put it back manually, but only with them knowing it was a tracking malware .....
Custom versions of Android from Samsung, LG and others are doing what Samsung and LG wants them to do. The Chinese versions of Android are notorious for tracking you and reporting it back to China every few hours.
Right now Linux offers the best freestanding device, security wise, but that choice is still monitored by whatever your choice of browser does.
(and you need to understand what that is, BTW)
Relatively comfortable pre-crinkled tin foil hats, anyone?