Poll: What rating System for FFA would you prefer?

It does not matter if it's +3 or +4 because you can adjust the elo factor to make it the same again. The numbers should only symbolize the relative difference between the placements.

I think the difference between 2nd and 3rd should be smaller than between 3rd and 4th this is why I don't Like +3 -0.5 - 1 -1.5 that much.

But maybe in between +3,5 - 0,5 -1 -2 is fine.
(or scaled to whole numbers: +7 -1 - 2 -4)

What would be the Best Rating System for FFA?

The Options we know are:
Solo +3 -1 -1 -1
FFA +3 +1 -1 -3
High FFA +3 0 0 -3

And @Radon and I both suggested a further Option:
Radon +4 -1 -1 -2
Empty +4 0 -1 -3

What do you think is best?
Do you have other Ideas?

Let me know!
Cheers Michael