The above is some pretty good info.
RR conversions are the best buy right now -- I have heard of several that sold in the $8-8.5k range in the last month. The market is soft right now, so it's a good time to buy. I expect prices will go back up a bit after the first of the year.
As far as makers, remember that few folks converted RRs to make safe queens: They were always intended to be shooters. And while the initial conversion quality varied, in the 18 years since the manufacturing ban, most of the RRs with "issues" have been fixed.
The lower receiver is a non-stress part of the M16 design, and about all you need to worry about is wear in the hammer and trigger pin holes. Worst-case, they can be bushed, or welded up and redrilled. A coat of moly and you are as good as new. It's almost impossible to spend more than $200-$300 on lower repairs, so condition has only minor impact on market value.
Whether the host receiver is cast or forged used to be an issue, but again, today I look more at condition and any needed repairs. Civilian owners rarely use transferable MGs in ways that will stress a lower to the point that a cast receiver will fail while a forged one won't.
A few other thoughts:
--I agree with amphibian: I only have an RR, and wish I had an RDIAS as well, to use in the applications he lists. But in the current market you are talking $2-3k more for an RDIAS, which buys a lot of accessories, uppers and optics. It is difficult to anticipate how you'll end up configuring an M16 -- I'm still inventing new setups -- but an RDIAS does have more flexibility. I don't feel limited with only an RR, though.
If you have more questions, or just want to talk M16s, shoot me an email and I'll send you my phone number. I'm always up for conversation.
And BTW, my apologies for not just answering you in my earlier post -- I was short on time, and I'm always trying to drum up traffic for my arfcom forum.
![Big grin :D :D](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)