Either Sword of War or German Greatsword. Both are the rarest 2h (well, those which you can buy and which people do loom at all), even if you don't like your choice you wont have any problems trading for anything else, most likely with big profit for you.
Wouldnt pick Highland Claymore, it's too short and notice its also slower. Great sword is a viable choice but the swing damage isn't all that great, so if I was a poky-guy I'd still choose German for extra range.