Just look at the specs and go from there -
Be Quiet Silent Wings -
Max fan speed: 1,000
Max sound Level: 15.5 dBA
Max airflow: 101.09
Max static pressure: 1.08 mm-H2O
Corsair MagLevs
Max fan speed: 2,000 RPM
Max sound Level: 16 – 37 dBA
Max airflow: 20 – 97 CFM
Max static Pressure: 3.0 mm-H2O
For all out cooling the Corsairs win hands down but for cooling while remaining quiet at low fan speed the Silent Wings win without a doubt.
The Corsairs win hands down for radiator cooling though.
I'm biased towards Corsair but honestly both are really good fans, If you are using them for a radiator I'd go for the Corsairs, If you are using them as standard case airflow intake/out-take fans then I'd go for the Be Quiets.