Best for the price - UTG Pro ACCU-SYNC Top Mounted Deployable Rear Sight

Seems heavy duty yet has a small profile. I like these much better than anything else of equivalent price. I love the push button for rapid deployment. I love that they lock in the open position so when manipulating around cover they are not inadvertently pushed down. Windage and elevation adjustments are solid and tactile. No side-to-side wobble when open. Lays pretty close to flat when in the closed position. Has 2 recoil lugs, takes up 2 picatinny slots.