Your average low-budget boat tours. However, this ...

Your average low-budget boat tours. However, this one stood out for me, because the captain of our boat was extremely friendly and quite funny (but not overly so). The journey was calm and relaxing, especially because it was in the evening.
I would recommend this service if you have a tight budget, but want to have a canal tour anyway. If you are not very fond of buildings, then take the tour at dusk or in the dark.