Ok I may be biased. My first job (as a full time engineer) was manufacturing copper wire telephone connectors. Our group also made the copper wire electrical connectors.
The 3M connectors require no wire stripping. Have excellent conductivity using a tin plated copper element. Accept a wide range of wire sizes. Require no special tools. A standard pliers works to crimp them, but I think the big boys just use their thumb and finger.
They are not reusable and we have to talk about value not cost.
Edit: I refer to the Scotchlok.