Sitting here today with both bikes being what they are and knowing what is known about each, the I'd buy a BMW in a heartbeat. All the technical reasons stated above plus a couple more.
While the GS has is issues for the most part they are all known and there are reasonable solutions for most of them. The Triumph is a new beast. While the motor maybe a known quantity don't think for a second that this new bike will not have teething issues. All new products do.
I personally don't like the looks of the Triumph frame. Also don't like the fact the rear subframe is not a bolt-on. Don't like the fact that Triumph couldn't (or didn't) come up with an original visual design. Blah, blah, blah.
At the end of the day, all the above is just a bunch of words. Buy the one that moves you.