My vote is either an Aimpoint w/ a magnifier, or a quality LPVO (Steiner P4Xi, Razor Gen2E, etc.). Which you choose is entirely up to your own preferences.
If you anticipate most of your use to be within 100y, it's hard to argue with the speed of a good RDS, and something like a T1/T2/M5/M5S will save you gobs of weight while still buying you insane battery life. A magnifier on an FTS base will allow you to use it when you want, and flip it out of the way when you don't. A QD version will allow you to remove it entirely when you don't need it.
If you anticipate a greater chance of shots beyond 100y, then an LPVO would probably be best. LOTS of options exist, so you'll need to wade through the trash to find one that's reliable and has a reticle you like. The new Steiner P4Xi has an awful reticle IMO, but the first gen is great, and the glass is very good for the price if you can find a used one less than $550-600 or so. People asking for $800 or more are up in the night for that optic, though. A little bit more than that gets you a used Razor Gen2E, which has better glass, a slightly better 1x (to me), and an additional 2X up top.
Me? I have both, and would choose the appropriate rifle for the job when I could. If I could ONLY have one, I would probably go RDS with a magnifier. For HD use, they make more sense to me, and as a civilian who would only use it defensively unless the world was literally imploding, I'd choose to avoid conflict whenever possible rather than stretch my carbine out to greater distances. I want to know I can make those shots, so I practice them when I can, but if I'm not forced to, I won't. Thus, an RDS seems like the more general purpose optic to me.
