My preference is Troy HK-style folding BUIS, but they aren’t cheap. I dislike the standard front sight on an AR15/M16 and prefer the HK globe for sight picture/alignment. The Magpul plastic BUIS are junk. I usually sell them as soon as I replace them with the Troy sights if they come standard on a carbine.
I currently have the HK style sights set up for 50/200 zero shooting on my 9mm CZ Scorpion and 100 yard zero on my AR. Both have optics, so the sights really are backup irons.
I may add them to my Tavor as well, though that comes with built in BUIS on the top rail, but it requires a special tool to adjust and they are awkward as heck to use. Again, prefer the Troy setup and like it standardized across all my rifles.