Rigid support insoles are the ones podiatrists and custom insole makers will recommend to you, like these Corefit moldable orthotics ($49.95 on Amazon), since they do the most to correct biomechanical problems. If you over- or under-pronate, have a pronounced difference in leg lengths (only 1 in 4 people have legs of exact equal lengths), or suffer from plantar fasciitis, these are the Foot Friends you need.
Soft support insoles are shock absorbers, pressure-point soothers, and optimal foot comforters (some of them are even made from memory foam). Though they can’t keep you in a pair of shoes that simply don’t fit, they can make your shoes fit a bit more snug and ~slightly~ extend the life of shoes with worn-out soles.
Semi-rigid support insoles, like these Powerstep Originals ($22.10+ on Amazon; pictured above), are in the middle of rigid and soft, a balanced and zen approach to the world of binary-minded insoles. Mostly, they’re used to enhance performance and response, so they fit in well with hikers, runners, and Moms who have to chase their kids at the grocery store (I was one of those kids, and still am).