Snails are actually really interesting creatures. I see mine do fascinating things all the time. For example, they have an interesting mating ritual. Some have extremely interesting patterns on their actual bodies, iridescent and colorful, outside their shells. They make zen like patterns in my substrate sand, and clean up waste fish food. I do not count on them to clean up algae or feces, but for cleaning up extra food, they work like a charm.
I truly enjoy them.
I have never owned shrimp, so I cannot tell you if they are a better choice. I have woned a crawfish and it was horrible. I ended up having to isolate it to it's own tank with no plants.