I'm on my 2nd R12GS, have ridden >120000km on both.
Con GS : the downside
on long hauls is the wind protection, and that's easily mended with aftermarket screens (or GSA screen if you like the looks). For fun stretches, I ride with a small screen. Don't need the extra range, because when the tank's empty I usually want to stretch my legs or have a coffee anyway. And when I'm riding in a group the GS's range is better than the range on my mates' bikes.
Pro GS : the GS is soooo nimble, sporty, flickable, it's really worth mentioning.

It'll outrun a GSA easy-peasy (assuming riders have same talents).
It burns less fuel.
It ticks all the boxes when it comes to travelling.
Con GSA : I've ridden the GSA on multiple occasions (when my GS is in for maintenance) and I simply don't like the ride. Don't like the looks. Wired wheels are a pain to clean. A fatty in Brussels' city traffic.
Pro GSA : in my book, as you will have guessed : none.
Actually, I don't 'get' the GSA : the whole industry is trying to fight off the weight, and I'd have to spend money to make a very nice bike heavier and harder to manoeuvre ? Duh. I'd pay for a lighter GS. The same reason I won't consider the Yamaha Super Tenere.
GS vs GSA is a bit like comparing a BMW 3-series with a BMW X3, both same traction, both same engine.
But ultimately it's very much A Personal Thing. Fortunately.