T-posts are metal posts that are shaped like a "T" while U-posts are shaped like a "U" if you look at them from above. T-posts are very reusable, have limited flex, and they are rather expensive. U-posts are affordable, lighter, more flexible, and are sold almost everywhere. T-posts use strong studs where U-posts use flimsy hooks that often bend or break off. This might sound like T-posts are better, but the studs require special tools like a T-post wire clip and a wire clip tool, where a U-post doesn't need any special tools.