Value for money leader is the 212+ at $30. It performs very well and is actually not to loud unless you are heavily overclocking the CPU and need dual fans at max RPM to keep it cool. A single fan on auto would be quite quiet.
The N520 is not a high performance cooler, but it is quieter. If you are running stock cpu speeds, the n520 will do a good, quiet job. If you plan to overclock, the 212+ will do a far better job.