SimGuruGrant a lead producer on The Sims 4 has released a tweet asking Simmers what type of stairs they would like to see be added in The Sims 4 in the future.
As you can see the most desired type of stairs is in fact Spiral. Also please note that this is not a direct tweet on them making the most voted stairs but it gives the developers on The Sims 4 a good idea on what Simmers want in The Sims 4.
Get voting simmers because your votes could count on any of these types of stairs being added into the game in the near future.