While Google uses a fairly straight-forward edition of Android on its own Nexus-branded devices, other smartphone makers can add their own apps and customize the interface to better suit their hardware; wireless carriers may add their own modifications as well.
Google’s own “pure” version of Android may run a bit smoother and faster because there is less tinkering.
However, it may not offer certain features offered by another phone maker or carrier, like a more advanced camera app. When shopping, be sure to check the software offerings as well as the hardware specifications for the models you are considering.
Because there are no third-party alterations to the system, Android updates for Google’s Nexus line tend to roll out more quickly than updates from other hardware makers and wireless carriers, which need to update or enhance their own modifications on top of Google’s changes for the new version. These companies also handle technical support for their own Android-based devices, while Google supports the Nexus phones and tablets.
If you do not care for the Nexus hardware choices, some companies like HTC and Samsung offer “Google Play Editions” of their popular phones that feature the stock edition of Android — and get system updates more quickly than other models. The Moto X and Moto G phones from Motorola Mobility (a company owned by Google) also feature a fairly unmodified version of Android with quicker access to system updates.