You're right, Afghanistan is/could be a great place for riding. You really should avoid getting any of the bikes that you mentioned. What you really want is riding by your Camp/FOB/PB/COP everyday:
That's right, an Iranian made 125cc Izmaray, complete with bubble wrap bling. Just go roll up a few sh*t heads, confonscate one of their bikes, and throw it in your quadcon with all of the COC gear you're going to be shipping home in a month or so.
So, who are you with? Where are you at? I'm guessing that if you are on a 12 month deployment you're stuck at LNK. Or maybe Deleram?
I was in a simliar situation as you last year at this time; getting ready to come back and wondering what kind of bike to get. I also have a Harley for what it's worth.
I really can't help you with your choice. I've ridden a BMW 1200 GSA, but that's about as far as my knowledge goes. If I had a choice (and the money) I would go for the KTM.
I was with 3/7 in Sangin. You were probably just arriving in country as I was leaving. I just got back in April. Went on Terminal in June and promptly started riding my Harley around the states. In October I jumped on my Honda and headed south of the border. I'm using all of my deployment money to fund a trip from Oregon to Ushuaia, Argentina on my bike. I'm currently writing this from a bar in Medellin, Colombia. I opted for a used XR650L. It's a great bike for Central/South America, but not very good on an American style freeway.
Good luck over there.