I own a SX and a SS, both of which are okay for singles, I also use the SS for doubles. The SX is just too head heavy for doubles, it really slows you down in quick point-blank exchanges at the net. Actually, I don't use my SX much at all, as I have a Ti-10 and a Ti-8, both of which have extra stiff shafts and are probably better overall for singles than the SX.
About three quarters of the doubles players at my club use the SA, it is by far the single most popular racket, even though it is a bit fragile. I've seen so many break, even fairly new ones, although Yonex have been pretty good about replacing ones which were less than three months old or so. One poor guy broke his in less than two weeks, and he didn't even clash it, he just hit a clear and the side caved in. They all go to big Yonex dealers for their rackets so I'm sure they're not counterfeit. The SA have light heads and the extra flex means you get a lot power on flick returns of smashes plus good control for drop shots, but I've tried it on lots of occasions, and if you rely heavily on the smash, you will not like it. It feels like there's nothing on the end of the shaft and you get little power on smashes.
I don't know anyone who uses the SR, and I've never actually tried one, but I guess it's a compromise between the SS and SR.
The best advice is to try before you buy if you possibly can. Similar rackets can feel so different if they have slight variations in weight, grip size, or flex, it's just not worth spending that much money until you're sure.