In a nutshell, DOT5 is silicon-based fluid, and DOT3 and 4 are glycol-based fluids. The main factor in brake fluids are their boiling points. DOT 5 is generally a better product if you don't change your fluid annually or biannually, because it doesn't attract water like 3 and 4 do.
Problem is, silicone is a "softer" liquid, and is around 2X more compressible than gycol is. So the pedal feel with DOT5 might not be as firm as with 3 or 4. But at the same time, it maintains much higher operating temp capacity, because it doesn't pick up the water that SOT 3 and 4 do, and the feel will be a lot more consistent over time. So like anything else, it's a trade-off.
Generally speaking, if you aren't tracking the car, and you stay on top of your maintenance (e.g. don't mind changing the fluid), then you'll probably get the best performance out of using DOT 4 and changing the fluid once every year or two. If you're one of those people who never change the brake fluid, then DOT5 will work best for you.
