Poster vs PVC
The basic difference is that PVC is much thicker than a poster (1/8th of an inch) and is solid. The benefits are it always lays flat, is more durable over time, runs no risk of forming waves or curls with humidity/temperature changes, and is a better surface for marking. Overall, it maintains a more professional look over time than a poster. I do the highest quality poster style available (polypropylene with a matte laminate), but I prefer the presentation and durability of the PVC.
These two maps are poster style that because of how they were hung and the temperature/humidity changes developed some wave/curl over time.
Poster Close Up
Here are 2 maps mounted on PVC, the first in two vertical parts and the second in two horizontal parts.