The DryConn Black/Blue waterproof connector large size are the most popular brand of connectors for 12 volt lighting systems.  They are a corrosion and waterproof connector made especially for 12 volt landscape lighting.

This large size is the best fit when heavy gauge cable is needed.  This wire nut has a maximum voltage rating of 600 volts.  The connector size of 1-1/4 X 13/16″ for copper wire type make this suitable in most applications.  In addition, this connector features a temperature rating of 221 degrees Fahrenheit and a silicone sealant temperature range of -45 F to 400 F.  As a result, this brand will stand the test of time.

Check out the Medium Black/Gray Connectors to fit most standard lighting applications.