Lots to choose from. itty bitty little V notch rear. 'Buckhorn' ........Aperture.
My least favorite is the V notch even tho I grew up on em. The Buckhorn is an improvement but still? not my cupa... Yep.. you got the V notch in it... then the sorta kinda aperture... then above that another odd long range wing thing.
The pure aperture... Basically a round hole you look through and put the front sight on the target. The human eye loves this sight. people who are learning to shoot love this sight. people who hunt or shoot moving stuff love it.
So what makes a good one? Well.. sight radius still matters some.. even with aperture. But what makes a good/great aperture? one that adjusts easily with clearly marked yardage on em. That is first. Then the sight radius. Then.. something useful in range finding.
The M1 Garand has all those things. simply a great sight. sooooo easy to use and adjust. Most do not know that the front sight (the only one you actually look at) is a certain width for a reason. A chest on a human is about 18" wide. At 200 yards the M1 front sight covers a human chest. You can do the math backwards or forwards from there.