I think this reviewer's impressions are a pretty good guide because he drove both transmissions in both cars back to back on track and filmed everything.
Here he's in the BRZ MT after driving GR86 AT & MT. He's talking a lot about the BRZ being "stable" "sticky" "slower / gentler rear slide" "BRZ can be controlled with confidence" "constant rear slide" "it's calm" "GR86 starts sliding here, but BRZ is stable" "BRZ slides little by little" "will not fail" "it is stable and can be operated with a margin" "GR86 is more severe when it slides" "BRZ is stable".
Here he says, "the difference is clear when comparing the images inside the car" "GR86 generates yaw in the high speed range" "BRZ is highly stable" "I feel that BRZ is easier to control" "the behavior on the curve is very different". Then he discusses the chassis differences and concludes, "these may be factors of BRZ stability" "the cornering of BRZ was wonderful".
I think he felt like he needed to bring it back to the middle a little, so here is says "on a tight curve, GR86 is easier to change direction and has higher controllability" which I guess means to can walk it out or in whenever you want, "but keeping the slide on longer curves requires finer control". So I guess he's saying if you like sliding, the GR86 would be the choice.
For me, though, I don't want to slide.

I want "calm & stable" when I'm in a fast curve on public roads....no "slide control" drama!

Here are a couple of corkscrew curves that I regularly zip through: