It's odd. For the longest time, I did not like the triangle reactor. The MK IV was definitely my favorite. Then, after seeing the VII go back to the circle in the movie, I was - much to my surprise - a bit let down. The triangle marked the progression of the technology with the new reactor which was a major milestone for Tony, arc reactor technology and the capabilities of the suits. The aesthetics of the reactor were kind of an, "out with the old, in with the new" statement. Not to mention the VI was a nasty piece of machinery. I'm not saying the VII isn't, and I really like the upgrades, it just felt almost like going backwards a bit for me.