I want to know what you think is the most UNIX similar OS to the original UNIX, about the User Interface, the commands, the way the programs work, etc
Well, I know this is not unix, but, if you want to use a running OS made directly by the crstors of unix, following the UNIX philosophy, you can try Plan 9.
In the linux world, people say Slackware and Void are the most unix linux distros.
It really depends on what you want, I mean the original actual user interface (that you could interact with) was just a tty with the thompson shell(I think). There are lots of similar unix-like OSes, such as SerenityOS, gnu/linux, *BSD, minix, etc.
Yes, I thought the most Unix-like os were BSDs, because there is no GUI by defect. But I mean, there are differences between them and I’d like to know which one of them is the most similar to the UNIX OS