Depending on your personal preferences and/or mission requirments:
Eotech
Or
Aimpoint.
Between the two they are the Best in quality, durability, and are both proven by extensive deployment by United States military, and many other nations, military forces. They each have their advantages.
I prefer Aimpoint myself, but a lot of that has to do with my vision. I do own both. Everyone prefers the battery endurance of the Aimpoints. My M3 I just changed the batteries for the first time, 5 years, and it is left on 24/7, it is on my go to Home defense carbine.
I have an Aimpoint M3 on my XCR, a micro T1 on my SCAR, a 5.12 Eotech on my Beretta Storm.
I just got a SIG 556 which comes with a fairly nice reddot of it's own. I plan on putting the SIG reddot on my S&W 522 22lr, and get an Aimpoint H1 for the SIG.
On all the Aimpoints I use Larue Tactical quick detach mounts. They do return to zero. On my Eotech, I only have the one, I use a GGG mount.
There are other products that work. None of them have the proven qualities of the Aimpoints or Eotechs.
Good luck.
Fred