If you want to enjoy always latest Android update Google Pixel and Pixel XL should be your first choice. Yes its google own phone produce by third party under google direct supervision. Previously Google use Nexus which contain pure Android DNA, mean now flashy customization like we use to see by Samsung Galaxy phones or others.
Some people like those customization as they offer extra functionalities on top of pure Android, but it comes with cost which is slow updates to latest Android OS version.
Google Pixel and Pixel XL are good phones check our detail specs and comparison here on GSMARENA.
Previously Nexus 6 was huge success for google pure android phone concept with Android L version.
Here is official video by Google.