Well the American version is the real Dennis the Menace.
The second one looks like a knock off of Calvin and Hobbes without Hobbs. Unless that animal in the corner is their version of Hobbs
They both debuted within a week of eachother, and neither is a knockoff, the UK version is called 'Dennis the menace and Gnasher' debuted March 17, 1951(on sale from 12th), the US version is called "just" 'Dennis the menace' debuted March 12, 1951 and was renamed 'Dennis' for UK viewers
Comments
The second one looks like a knock off of Calvin and Hobbes without Hobbs. Unless that animal in the corner is their version of Hobbs