-- revised 2/10/2017 --
The white spring clips are cheap, easy to use, fairly secure, not waterproof. I've had some of the 2-wire type for a year. They are useful while you are messing around. Generally better than alligator clips.
The lower set are pretty much the opposite: secure, waterproof and not cheap. And once you snap one of these suckers together it's work getting them apart. But really waterproof. Also, they could use a screw-down hole like the white clips.
REVISED: The spring snap closures (right end of black connectors) are brittle in cold weather.
The search goes on...