If you want a red dot, the Trijicone SRO is a nice sight. It has a bigger window than the RMRs and it's significantly easier to pick up that dot quickly. It's a little less expensvie than the RMRs. I've read that they are aren't as robust as the RMRs but I've never seen or heard of one breaking under any sort of normal use.
I don't look at an RMR as having a sight window...its more like a frame with a glass and it suspends a dot.
I like it's small size I shoot mine both eyes open and I'm more looking around it that sighting through it.
