Deb Tucker's Wing Clippers. There are two different ones, both make many sizes.
Until I started using these, my geese may or may not come out the right size. Often one corner or the other didn't come up at the right angle, leaving my geese wonky and my seam too scant.
With the Wing Clipper, you do make them a bit oversize and trim. That extra step and little bit, though are worth it to me as they come out perfectly every time.