My pins are all curved. I have two sizes - smaller and larger - and it depends on how dense my quilt is which size I use. My pins are all stored open and I simply dump a pile on the quilt and shake them apart.
BUT, I HATE pinning and think I'll try spray basting.
Here's a great pinning tip from KLue
http://www.quiltingboard.com/posts/list/20874.page