Hiya Boldnee!
All car seats sold in New Zealand conform to one of our accepted safety standards. So they are all definitely safest. Some may perform differently and offer different features over another but it's impossible to say which is safest.
This link
http://www.car-seat.org/showthread.php?t=37085 has a review on the Brio Zento. You'll be able to find numerous reviews on the Cosco Scenera via google.
It's kind of comparing apples with oranges unfortunately, they are two entirely different safety seats, you just can't compare.
Hope this helps!
Feel free to email me if you need further assistance
