Neither. Your collection has a fixed size and std::array is sufficient.
The data structure you implement is called a ring buffer. To implement it you create an array and keep track of the offset of the current first element.
When you add an element that would push an item out of the buffer – i.e. when you remove the first element – you increment the offset.
To fetch elements in the buffer you add the index and the offset and take the modulo of this and the length of the buffer.