well here you go my ideas for what they are worth from this side of the pond.
I currently have both a GS (ok an old 1100) and a 990.
The GS is the best long distance tourer, the KTM is the better handling and quicker and most nimble.
The GS has better gas milage, but not by much, the KTM is about the same if ridden in the same way, however it appreciates being ridden harder and is fun so you do, and the tank is much smaller, so less milage to the tank. However if you ride it like you would the GS at the revs of the GS then the gas milage is similar to the gallon, ok not quite as good but not far off.
Your big problem is that the GS is to be replaced by the Water cooled one and the 990 by the 1190 so you will be looking at second hand for both.
If you want to long distance tour most then the GS, if you want a bit of off road/dirt track then the 990.
If you want to work on the bike yourself then get an older 1150 GS, it has "normal electrics" it is simple and easy reletivly cheap and you can find a good one with a selection of extras at a good price.
The 990 is easy to maintain, but more time consuming, due to the way its put together, normal electrical system, but chain drive.
The 1200 is easy to maintain for most jobs, however if the rear diff goes then its a workshop job at best or a new one and very expensive, and electrical problems are a PIA due to the canbus electrical system.
The super ten is a good solid bike, comfy (although I have only ridden one a couple of times), dosent have canbus but does have flyby wire, and abs, traction control, linked brakes etc all controled by one central electronic unit (damn expensive when it goes) however shaft drive simple and robust.
It comes down to being honest as to the use you are going to make of it. My GS is by far and away the best all round long distance bike, I have both but if I had to have just one then it would be the 990, its easier to make the 990 a comfortable long distance tourer (even if I end up buying big tanks) than it is to make the GS a good offroad/dirt tracker, not that the GS is unuseable on dirt, its just that the 990 is better. I am 6'5" and the extra space on the 990 is nice and it being a tall bike is also an advantage.