Honestly, the easiest urban trash bins to clean graffiti off are smooth stainless steel and powder-coated metal bins, especially ones with a factory anti-graffiti coating. The surface is non-porous, so spray paint and marker tend to sit on top instead of soaking in. A warm soapy wash, a little citrus or solvent-based graffiti remover, and a soft pad usually do the job. If you use a pressure washer, keep it gentle so you do not dull the finish.
Powder-coated steel or aluminum is a close second. The coating gives the bin a slick shell, and most graffiti wipes off before it fully cures. Look for a smooth gloss or semi-gloss finish, not a rough textured one. Smooth HDPE plastic bins can also be fairly easy to clean, but only if the surface is not deeply textured. Textured plastic traps paint in the grain and turns a quick wipe into a scrubbing session.
I would avoid porous concrete, rough-cast metal, and heavily textured composite bins in graffiti-prone areas. They look tough, but they hold paint and require more labor. Even with a protective coating, concrete often needs re-coating after aggressive cleaning. So if I were specifying bins for a city hot spot, I would choose smooth stainless steel trash bins or powder-coated metal bins with an anti-graffiti coating, plus removable panels or wraps so damaged surfaces are cheaper to replace. That combination makes graffiti removal faster and keeps the bin looking decent between cleanings.