The second sentence has more momentum because 'Although' immediately tells the reader that the main point of this sentence will follow and contrast with the opening phrase. Thus the reader is encouraged to read 'The Glasgow ECC can serve as a model of city marketing techniques' quickly in order to get to the main verb phrase. Moreover, because the reader knows that a contrasting point will be made, the reading of the opening is modified and directed. In contrast, the first sentence gives no hint of where it is going. 'But' is a sudden change of direction.