You´ll see more using a bus but they rarely travel scenic routes because they´re designed for locals & Tour Buses are incredibly expensive, although great for getting a quick overview of the key sights. I find working out local bus networks & the often baffling ticket & validation systems more trouble than it´s worth - unless I´m going to be there for some while. In Paris´gridlocked streets it´s often quicker to walk than ride on a local bus.
Barcelona has such wide, arrow straight that look intimidating to cross, they're 2 or 3 times the size of any London street - yet it's the most pedestrian friendly city I've ever been in. Pedestrians get priority at all junctions & traffic always stops.