Why are drops round?
It is simple: because in nature things tend to rest in the position that consumes less energy. Solids tend to rest with its heaviest part at the bottom. Liquids form spherical drops because that is the shape in which its molecules attract to each other with the most similar strength.
Now, you should know that, in our planet, it is almost impossible to find perfectly rounded drops naturally. Why not? Because of density. gravity and resistance. While in rest (in dew, for example), gravity affects liquids making drops slightly more rounded at the bottom. While in movement (in rain, for example), drops begin tear-shaped because of their resistance to fall; then they form spheres, but air resistance tends to push the bottom of the sphere up, causing the drop to first become like a disk and then to break into smaller drops which repeat the process.
Something like this: