The Jazz is the most practical and usable of the 3, the fold flat seats means it can easily hold as much as most of the CUVs on the market. I've been able to fit more in one than a Toyota Land Cruiser. It also doesn't feel slow with the CVT, as it's a surprisingly lightweight car.
The Mazda is the most fun to drive, and has the most "smart" safety features like auto braking, lane departure, etc (depending what trim level you buy). It's the best looking of the 3.
The Yaris splits the difference, not as useful or fun to drive.