I happen to have several.
From C-More to UltraDot, to Burris, to Tru-Glo, & one other brand that escapes me right now.
If used properly,, they can be excellent.
For serious accuracy,, get the smallest MOA dot offered. As distance increases,,, the dot appears bigger,, so it can completely block out a small target center.
For speed,,, a bigger dot can be picked up quicker,,, and be very, very fast in hitting a larger target. (Think competition here.)
I just took a Burris off a handgun to put a scope on it instead. Why? I'm taking this gun along on an elk hunt this fall, and in practice at 100 yds,, I "lost" the target center so much, my groups were enlarged. A scope allowed me to get back to serious accuracy.
If you are looking to compare brands,, then I'd give the nod to UltraDot or C-More.