As a (mostly) outsider looking in, from a game design standpoint, the first 4 are the best. Simple arcade style gameplay that you can pick up and just play for 10 minutes. Sister Location deviates from this to deliver largely scripted events, which is less fun in terms of replayability. Help Wanted 1&2 and Fnaf 6 are pretty good on the arcade gameplay and Fnaf 6 expands upon it with its tycoon segments, so I'd place them both above SL. Security Breach couldn't seem to decide on a story and wasted a good villain, and Ruin was pretty much just a better version of it that set up future installments.

My ranking would probably be:
1. Fnaf 1 and 4
2. Fnaf 2 and 3
3. Fnaf 6
4. Help Wanted 2
5. Help Wanted
6. Ruin
7 and 8. Sister Location and Security Breach (Couldn't decide which one to place last. It really depends on if you like SL's solid story or SB's scope as a game.)

Where is FNaF world and Freddy's in space?

aww so cute i feel like imma die here of how cute this is :D

Yes sl first >:D