So we spent our fist (half) day at Monterosso's beach. It was marvelously refreshing, though we soon realized that this holiday was going to be way different from our Engadine trip. Can't say we hadn't been warned, but to be honest it's difficult to imagine a place being so touristy.
Monterosso has the nicest beach of all the villages, and the only proper beach to be honest. We loved the other villages (more on that later) and their little nook-like beaches (more like crevices in the rock), but if you want to have a real beach day (and save traveling costs), Monterosso it is.