The main difference between a 3 blade and 5 blade ceiling fan is its look and noise. It is quieter to have a 5 blade ceiling fan because more blades tend to create a natural balance within the fan. As for air delivery performance, both 3 blades and 5 blades ceilings are comparable in real-world performance and there isn't much difference between them, you shouldn’t put too much concern on blade numbers affecting the cooling performance of a ceiling fan.