TCP connect scan is regarded as less stealthy because it completes the three-way handshake, making the scan more detectable by security devices. A SYN scan, however, is more discreet as it sends a SYN packet and if a SYN-ACK is received, it does not complete the handshake but sends an RST instead. This behavior is sometimes referred to as a 'half-open' scan because it doesn't establish a full TCP connection, thereby reducing its footprint and likelihood of detection.