Any types of buttercream are stiff enough to pipe the patterns I shared in this post, but if I have to pick one, I recommend Swiss buttercream. The detail: It depends on the recipes, but the very stiff ones are Swiss, Italian, and American buttercream, in my opinion. For Italian and Swiss buttercream, the meringues are the key to making them stiff. And Swiss meringue is more stable than Italian meringue since it's cooked with higher heat. Therefore, the buttercream stays more stable even hours after it is made. American buttercream is also very stiff. But it is very, very sweet. And it is slightly more sensitive to heat since it's a mixture of just butter and sugar. So! To sum up, I think Swiss buttercream is most suitable to pipe, especially for more fine, detailed decorations. It is solely from my experience, but I hope you can take it as one opinion!