Security: PortSentry vs. Snort Comparison

Snort
Snort falls into the category of Network Intrusion Detection Systems (NIDS). It is the best open source program of this type that I am aware of. Port scan detection is a subset of NIDS so one can rightfully assume that snort handles this as well...

Port Sentry
A port scan detector that can be configured to bind to ports you want monitored, reporting scans made to these ports and optionally running a command to deal with the scanning host (usually in the form of routing that host to a blackhole or adding a firewall rule dealing with said host)...