RCSB PDB - how to choose between multiple copies of the same protein?

I want to map the location of missense mutations on a protein, `SERPINB3`. I intend to do this using [PyMol](https://www.pymol.org/) and download the protein structure from [RCSB PDB](http://www.rcsb.org/pdb/home/home.do). However, searching for `SERPINB3` reveals two molecular structures (as well as one homolog, `SERPINB4`). 


One of the structures, `2zv6`, presents the protein as a multimer of three identical chains. This structure is older (2009) and is used by computational tools on CbioPortal.


Another structure, `4zk3`, presents the protein as monomer and has been more recently published (2015). 


I am inclined to trust the more recent protein over the older one on the vague notions that:


1. Its newer so it was probably an improvement in terms of some aspect of the structural determination process
2. I've heard that its "unusual" for a multimer to form with three identical chains


...which are not particularly good rationalizations. 


I have not found any literature comparing these competing molecular structures and honestly I am not entirely clear on how different they are from each other beyond the fact that one is presented as a multimer.


**What justifications can be made based on chemistry and/or biology to support one of these structures over the other?** I am interested in both choosing between these two structures and in general good practices for choosing between two competing structures. 


