For me, the Oura was the better ring, but that's because I solely wanted a sleep tracker to help me perform better the next day. The problem is, using it as a fitness tracker doesn't really work, it does measure your daily activity but purely to find out when you should sleep.
The Motiv Ring, on the other hand, is slightly different; it performs best as a fitness tracker, with an element of sleep tracking. So really it's down to personal preference.
To find out more about smart rings, you should check out my buying guide.