"sdiff" a very useful utility to compare the result side-by-side. For example, I can compare the output of the 2 nmap results as below:
$ sdiff -bW <(nmap -sV -p 80 192.168.31.1) <(nmap -sV -p 80 192.168.1.254)
 |
| Comparing port 80 |
A more complex example, such as:
$ sdiff -bW <(nmap --script ssh2-enum-algos -sV -p 22 23.96.21.205 -Pn) <(nmap --script ssh2-enum-algos -sV -p 22 127.0.0.1)