I use Shimano roller brakes on my "city bike" (Redline R530) The stock front brake was the anemic IM-41F. I would not recommend that one to anybody. I now have upgraded to a dyno hub with the IM-70F which does a much better job of stopping. I have only ridden a couple of disc brake bikes, but my general take on them is that they are very powerful and should stop you in most if not all conditions.
Roller brakes are totally enclosed and are not affected by weather at all. Discs are affected at least a bit by nasty road conditions.
Another problem with roller brakes in the US is availability. I have had to source parts for mine from the Netherlands when I could not get items from any US distributor.
I don't believe they offer Alfine with roller brakes only discs and those are hydraulic discs in the US. The roller brakes seem to only be compatible with the Nexus hubs.
I like my roller brakes fine and they stop me and my fully loaded bike with no fuss at all. FWIW I seldom exceed 15mph and my fully loaded weight is ~300#. YMMV
Aaron