What 762x51 said......
I sold my Bushmaster Ak-shorty summer before last because I was offered about $200 more than I paid for it. (I also couldn't entirely fianance the S&W Super-9 NIB w/3 barrels that I got, w/o selling the Busy- so, I couldn't resist)
That left me with my flat-top heavy match bbl upper w/freefloat tube foreend.
I waited a while to replace it to see if AWB would sunset. (It did!)
I got a RRA to replace lower because of less wait and lower price than Bushmaster.
I got the complete lower assembly for $240 out the door.
I've put a J-P single stage adj. trigger back in it (removed from Bushy before sale, along with my ambidextrous safety and DPMS target grip.
Now I'm back to shooting my 1/2" groups with my AR upper!!
I did not even need the rubber tightening bushing to prevent upper-to-lower wobble, reciever is VERY TIGHT. Magazine well is also tighter than any other AR reciever I've dealt with (Colt, Bush, DPMS, Olym).
Also, the KUH-SPRONNNNNNGGGGGGGG of the Bushmaster is a kuh-spronk! with the RRA. Much less annoying spring twang!!!!! Noticed that at the very first shot.
My vote goes to the RRA.