It's neither. It's partially fixed. Depending on the bending stiffness of the column, and the rigidity of the base plate, the base plate connection to the foundation, and the foundation itself, it may be almost rigid or almost pinned.
The simple approach that eliminates the need to quantify the degree of fixity, is to design the base plate and its connection to the foundation assuming it is fully fixed, and design the columns, beams, and other components of the frame assuming a pinned connection. IF you need some fixity in order to make the frame design out, then you'll have to quantify the partial fixity provided.
