There are many variables that go into choosing the correct insert for your turning operations: insert shape, geometry, grade, and more. The goal is to select an insert that meets your requirements for quality and performance, while providing good chip control, and a reasonable combination of wear resistance and toughness.
Choose the insert style (shape and size) based on the features of the part and the desired depth of cut. A larger nose radius is stronger, but requires more machine power, and increases the tendency for vibration. A smaller nose radius increases the access to fine part features, but has a weaker cutting edge.
Choose the chip breaker (geometry) based on the selected machining operation: finishing, medium, or roughing. Roughing with high depths of cut and feedrates requires an insert with a stronger cutting edge.