For a radiator, you want a fan with high static pressure. Yate Loons make great case fans, for instance, but lose a lot of their airflow once there's any restriction.
Generally speaking, sleeve bearing fans have less bearing noise than ball bearing fans, but have significantly shorter lifespans when mounted horizontally, due to how the bearings self-lubricate.
I'm not familiar with the stock fans, but Noctua's fans are never a bad choice in terms of noise characteristics, though they are a bit pricey. Check out Noctua's site to find the fan that is most suited to your needs.
Remember that higher max airflow doesn't necessarily mean that a fan will be any louder than another with a lower maximum, when pushing the same amount of air...