The older castello's had a diamond in the stem and the more recent ones have a bar. The shape is really up to you to enjoy, we will enjoy your happiness with the briar along with you but our taste on any particular shape should not matter. Castello's are well regarded pipes with aged briar.
Perhaps more importantly than the shape is who your purchasing it from. There are site sponsors that I wish I would have started buying from when I first started, rather than learning a several hundred dollars lesson.