1S or 4S are both fine.

One would open 4S because if the opps had a constructive sequence to 4H, there's no way you wouldn't bid 4S as a sac at these colours -> may as well make it difficult (read: virtually impossible) to play 4H on the board.

The downside of opening 4S is that sometimes you catch partner with an awkward strong hand and 2 small in one of your singletons and miss a slam that you'd find if you opened 1S.

The relative frequency of these two actions make 4S a winning bid, I believe it's clear for both MP and IMP scoring. Other boards may not be so clear, so that's always also a good thing to include in polls like this one.

I note that this hand is no longer first seat, as it was when you first asked the question...

1S 4S is inconsistent, North should probably rebid 3S given that they've opened 1S.

Given that you know you're off lots of Kings, and you know that you don't have much communication to partner's hand; I don't see what the rush to play in NTs is.

You know partner has the AS, not the KS, and enough spades to commit to playing in 4S opposite no promised support.

You know that partner doesn't have the KC and may well not have the QC either. 

Where are your tricks in 6NT going to come from if neither black suits behave?

I would sign off in 6S, and if it's the wrong strain you can tell partner to not commit to playing in game in spades opposite a negative double when their suit isn't self-sufficient.

Thanks! interesting!