For sights that can be used for defense and/or competition, I recommend 3-dot sights. Of those, Ameriglo Operators in any color combo you prefer.
I have green on green on one gun and yellow rear/green front on another and really like the yellow/green but can make do with either.
I like that the front night sight vial is highlighted with white paint and the rears are not on the Operator sights. I used my Glock 19 in IDPA with these sights for months with no issues whatsoever. And the real plus there was that I was training with the very gun and sights that I carried.
As far as the Straight 8's go, you'll have to try some out and decide. They 'are' quick to pick up to the eye and it's very easy to stack them, but you lose the advantage of precision with them, in my opinion.
You can easily line up 3-dot sights and maintain a degree of accuracy whether the target is up close or farther out.
I think Straight 8's are great for up close defensive purposes, but beyond very close range, the degree of precision aiming is compromised due to the stacking of the dots vertically as opposed to lining them up horizontally.
It's easy to be off slightly to one side or the other or to misjudge the space between the top and bottom dot and be aiming higher or lower than intended.
The eye tends to take more time to line up the two vertical dots precisely than it takes to line up 3 dots horizontally.
My competition-only sights are actually a Glock white outline rear with a Fiber Optic front. But that's just me and I wouldn't recommend that for a defensive sight configuration.