My honest take is that side-opening urban trash cans work better in some busy public spaces, but top-opening ones can be better in others. It is not really a simple side vs top question; it is about how people actually use the bin and how the city maintains it.
Side openings are great for busy sidewalks, parks, transit stops, and event areas. People can drop waste in without touching a lid, which reduces the ick factor and encourages use. They are also easier for children, older people, and some wheelchair users because the opening is at a comfortable height. When the opening is large and well placed, people are less likely to leave coffee cups or wrappers on top. But side openings have downsides: rain can get in, wind can blow litter out, and odors or pests can be a problem if the bin is not emptied often. Low side openings can also overflow and look messy.
Top openings, especially with a hood, flap, or small mouth, can keep rain out, hide waste, reduce odor, and make scavenging harder. They often look tidier in narrow streets and near cafes. The trade-off is convenience. If the opening is small, high, or hard to use, people will leave trash beside the bin or stack it on top. Lids and flaps can break, get sticky, or be propped open.
So my answer is: side openings often work better for getting waste into the bin in high-traffic pedestrian areas; top openings often work better for weather control, odor, and pest resistance. The best urban bins usually combine both ideas: a side-facing opening with a rain hood, a self-closing flap, good height, clear signage, and durable materials. Capacity and emptying schedules matter as much as opening direction. A beautiful bin that is emptied twice a week will fail; a simple bin that is easy to service will usually win.
If you are choosing for a city, test a few designs on the same block. Watch where people put their hands, how often the bin overflows, how much litter appears around it, and how easy it is for workers to empty. In most cases, the “better” design is the one that fits the street, the climate, and the collection routine—not the one that looks best in a catalogue.