I test road a R1200GS in 2009... didn't like it. Bought a FJR.
I test road a R1200GS in 2013... loved it, put down my deposit on a 2014 model.
And buy the old one because the mechanic has more experience working on it... really?
Ride both, check you bank account and buy the bike that makes you happy. My personal opinion that the new GS is freaking great and the old GS was a POS that I would never own at any price should have no effect on you.