Wo-flute end mills are designed for efficient material removal, typically used in softer materials like plastic and aluminum. We recommend using them in situations requiring deep cuts and higher feed rates. On the other hand, four-flute end mills create cleaner finishes due to their increased cutting edges. They are better suited for hard materials such as stainless steel and complex composites. However, they tend to have lower chip evacuation capacity, which can cause heat buildup during operation.