Hi mate. Im down in stoke on trent. I have a mate in cheadle. Rides a honda vtr firestorm.
Man, im going to get so flamed for this reply! Lol
Anyway with reference to your questions, i guess its down to preference. But not only that, its down to what you want from your bike, what you will be using it for, how tall you are and how much coin you have to spend!
I personally think the 1200gs is a bike aimed for middle age business men having a mid life crisis that involves being a wannabe ewan or charlie and copious amounts of just for men!

it reminds me a little bit of people who buy toyota prius cars. Lol
The 1200gs adventure is the same really, just taller and more expensive. Again the afore mentioned mid life crisis bunch buy em and never go near a dirt track, or a foreign land for that matter! Lol. Pointless. They are bikes for the people who buy into the gs 'fashion' in my opinion. They are less rugged, less pure somehow.
Both 1200 bikes will perform well, but for the real deal you need an 1150gs /gs adventure or maybe an earlier 1100 gs. Those bikes were built for the job, built to conquer the world, long before ewan and charlie were in the forefront of public opinion.
All i can suggest is riding a few, and taking a good hard look at what you will use the bike for. Both the 1200 and 1150 have good and bad points. Its subjective at the end of the day though. I love the 1150's. Some love the 1200's.

just a thought though, look how many 1200s are up for sale compared to 1150's. That might tell you something! Lol
Take it easy
Matt