Heel flap and gusset. Though my main reason is that I enjoy the process of knitting it. Also great for those new shoes with a tight back, protects your achilles quite well
I have only done one and a half pair of socks, but I really like the shadow wrap short row heel. It fits nicely and it's not too difficult to do once you get the hang of it! But it does take some work with the knitting together so you don't get holes