I’m lucky enough to have flown in both both business and first (upgrade!) on a 747, although a long time ago. The front was a bit more spacious, and since there is no cockpit in front it feels quite different to upstairs.
The upstairs business class cabin on the -400 was also larger (more people flying) if I remember correctly. A lot less people fly first than business.
In first you are ahead of the front wheels, so when turning during taxi, it’s quite an odd sensation.
The nose of the 747 is also very quiet; you are very far forward. It's also private as there's no through traffic - you turn left on boarding through 1L and there's only First there.
The upstairs business class cabin on the -400 was also larger (more people flying) if I remember correctly. A lot less people fly first than business.
In first you are ahead of the front wheels, so when turning during taxi, it’s quite an odd sensation.