Definatley the chest piece. I spent three days on it, taking my time to make sure it was as perfect as I could make it. Got it built, had some warpage problems, then got it resin'd, glassed and some bondo, and then realized that I had used a very early file that didn't have the ab plate that went with the chest piece uniformly. I still haven't re done it, but have built two helmets, shoulders, biceps etc since then.....still not looking forward into building another one