Pad 1: Very aggressive friction coefficient, max braking performance, aggressive disc and pad wear. Pedal modulation can be tricky if out of temperature or as it wears down. Use in hotlap and qualifying sessions, sprint races and can withstand 3 hours races. Risky and dangerous to use over 3 or 4 hours because the pads will wear down, overheat and lose linearity in brake pedal feel.
Pad 2: Very Good friction coefficient, very good braking performance, good disc and pad wear. Pedal modulation almost always good and linear, good feedback while overheating and gradual wear. Perfect for endurance racing, but can also be used in hotlap , qualifying sessions as well as sprint races as what it loses in performance, regains in braking modulation and predictability. The default choice for long endurance races, easily makes 12 hours and can make 24 hours race too with a bit of care. Will also overheat and lose linearity in brake pedal feel when worn out, but in a more predictable way and after much longer stints. Because of the lower friction, you could possibly use smaller brake ducts.
Pad 3: Moderate friction coefficient, braking zones can be longer in dry, very moderate disc and pad wear. Excellent pedal modulation also in cold ambient conditions, very linear pedal feedback. Excellent choice for wet conditions and very long endurance races. Very predictable and easy to modulate brake pad. Because of the lower friction, you should use smaller brake ducts.
Pad 4: extreme aggressive fiction coefficient. Max braking performance, extremely aggressive disc and pad wear, bad cold performance. This is a sprint race pad that can last about an hour but will show worse pedal feel, worse performance and overheating towards the end of the one hour stint. Those kinds of pads are not used in endurance racing, but included for demonstration purposes.