Final answer:
The stealthiest nmap scan option is the Idle scan, performed with the command nmap -sI, as it uses a decoy to mask the source of the scan.
Step-by-step explanation:
If you wanted to perform a scan with nmap that offered the greatest amount of stealth, the option you would use is nmap -sI. This command initiates an Idle/stealth scan technique. What makes this method particularly stealthy is that it uses a decoy to perform the scan, making it appear that the scan is coming from another host. The intention is to obfuscate the true source of the scan. This can be useful in avoiding detection from the target's network intrusion detection systems (NIDS).
Other options like nmap -sN, nmap -sS, and nmap -sX are also types of nmap scans. The -sN option conducts a NULL scan, -sS performs a SYN scan, and -sX carries out an Xmas scan. While these can also be used to reduce the chances of detection, they are generally more detectable than an Idle scan due to the types of packets they send and the behavior they exhibit on the network.