WHERE DO I GO FOR SOBA? Sarashina-Horii or Minatoya?
Just to make sure you know, sarashina soba is nothing like regular soba. To make sarashina soba you need highly refined flour that has no buckwheat taste, aroma, or color. The question of whether or not sarashina soba is good aside - if you are only going to eat Japanese soba in one place it should not be sarashina soba because it's not really representative of "normal" Japanese soba.
You mean the Minatoya near Toranomon, right? Then it depends whether you want to go new school or old school, I suppose. I've been to Minatoya and enjoyed it - not the best soba in town, but it's a stylish setup. I haven't been to Sarashina-Horii, but it looks more traditional and has a much broader menu. http://tabelog.com/tokyo/A1307/A130702/13001226/
To be honest, there are much better soba shops around, so I'd suggest doing a search on the boards for ideas. Personally, I'm fond of Tamawarai (玉笑) near Meiji-jingumae station. http://tabelog.com/tokyo/A1306/A13060...