If you are considering the Armor, you might as well get the stacker. Now you just have to decide on if you really need a case that big. If you plan to do some serious watercooling and want everything internal, get the stacker. If you plan on having a hell of a lot of drives, get the stacker. But if you just plan on having a nice simple gaming PC I'd go with the P180. Personally I'm in love with it right now and am considering getting one for my new rebuild soon. So ask yourself if you need a full tower or just a large mid-tower? I would think that would make it easier.
I have a P180 and its great for what both the above posters have said, a good, simple gaming PC. It can hold 6 HDDs internally, and I'm sure you could shangai a WC setup into there as well, but the Tri-Cools included provide good airflow, and you can mount extra fans if you wish. I'd ditch the VGA duct though, not terribly useful IMO.