All things being equal, I frankly prefer the size of the GA from a comfort standpoint; the lower bout of the GS is just slightly bigger, and the corner of the guitar tends to dig more into my upper arm muscle. I also prefer it from a sonic standpoint too -- with one caveat...
I know Taylor promotes the GS as their strumming guitar -- which is primarily how I play, so you'd think I'd be drawn to it over the GA. But in the 6-string version, the GS sounds a bit too 'boomy' to me. Not really 'boomy' in a bad sort of way; just a touch too much bass response for my taste. I can almost come to terms with it -- until I play a GA, and everything just sounds more balanced to me. My brother has one of the BR-VIII guitars (Cedar/Claro Walnut), and I personally find it a too bit 'warm' for my taste -- which I attribute to both the wood combination and the GS body. I've played other Walnut guitars with various types of tops (['Sinker'] Redwood, Walnut, and Spruce) -- all in other body styles (GC, GA, and GO respectively) -- and my impression of Walnut was a bit more favorable in the smaller-bodied guitars.
Then I move on to a 12-string; and suddenly, I get it with the GS. I think I tried one GA 12-string when I was buying my first Taylors, and remember [literally] wrinkling my nose at it. Then Joe at Empire Music handed me a 656ce, and I knew I'd found my [first] 12-string. The extra bit of bass from the GS body just seems to compliment the octave strings perfectly, particularly with the Maple body. My K66ce and Custom GS-12 -- same kind of thing. And when speccing it out, I decided to spring for the armrest on my Custom GS-12 to mitigate the minor discomfort of the lower bout.
So my short answer to your question, Susie, is: I like nearly any GS-bodied 12-string... But prefer a GA-bodied 6-string...