Unflinching has a very small effect at any rate and it's even smaller with Ambush. Ambush increases stability and weapon handling though so it's still a good option. It's my personal favorite sight.
Most people prefer Shortgaze though. It's got the same zoom as Ambush, reduced stability and weapon handling but increases aim assistance and wiggles less when you strafe (also cooperates a bit more with Unflinching).
That's a really good PvP roll, but it's all a matter of preference at the end of the day. Try them both out and let us know
My personal favorites are Ambush, Snapshot and Double Down (have this on my LDR). A lot of people vouch for Sortgaz/Hidden Hand/Unflinching. I have that roll on my Benevolence but always come back to my LDR. Without Snapshot I feel sluggish and the extra ammo from Double Down is hard to pass up.
My point is, play around with different stuff. You might end up with a very different preference than the so called Tier 1 rolls