Strangely the iPhones voice recognition is awful compared to the Apple Watches. At two weeks I've now used SIRI more on the watch than all the iPhone models in the last four years (since SIRI introduced) combined.
I will say the original Moto X (which had a slightly modified Android version - to constantly listen for instructions) voice recognition system being trained and locked to a single individual probably has advantages in most situations (including accuracy), but not all. As a secondary phone (web testing) family was excited to use it as an Amazon Echo-like, or [we were really thinking] 2001-HAL/Alien-Mother-like, always on fun answer machine. Then we realized it only worked with a single persons voice.
Then again things didn't work out so well for most of those using HAL or Mother.