Both to be honest. I have some hilly ground that I can't pull the 6 metre roller up for tillage so was going to use it on the ploughing there.. plus I want to take advantage of the tams so I thought it might be the best option to go for.
If it were for tilling ploughed ground for cereals only I would be inclined to go for something with a smaller disc than a Rubin such as the Vaderstad that you mentioned but if it is also going to be used for deeper work then you are probably right to be going for something with a big disc.