To me the vader helmet in Esb and rotj the face has an almost "shocked" expression. Deer in headlights. He looks much more serious/focused/ in his ANH helmet. But I agree, with more exposure of the chest armor it creates the illusion he is wider. With the under robes over the chest plate he looks narrower cause it blends with the fabric from the cape, making his shoulders and chest seem less upright and narrower.ESB, the shoulder armor uncovered and the changes to the helmet make him look more menacing than ANH (except the loss of the red eyes). Not a huge fan of the smaller dome in ROTJ.
Seeing the internals of the helmet in ROTS as first built was really cool as well.
I think that is the case for most people. The version of Vader most replicated in popular media etc is the shiny more refined esb/rotj look. Casual fans wouldn't be a able to notice a difference between those two, where as ANH looks distinctly different to the casual observer. I think most casuals would be more awe struck by nice ESB/ROTJ costumes because that is their pre conceived expectation being met.ESB. Whenever I think of Vader, even before knowing what the difference between the movie suits were, it has always been the ESB version that I imagine. If were talking details, I prefer it over ROTJ just for the extra greebles on the chestbox and the dome shape on the tip of the mohawk.