We use both Ancor and 3M ring terminals, butt connectors, etc. Here's my take:
are suitable for double-crimp treatment, using a special double-crimp tool. Generally, they are very good and are -- by themselves -- perhaps more robust than the 3M heat-shrink terminals.
The 3M heat shrink terminals
require a special crimper also...one which will not damage the heat shrink (else, why use heat shrink terminals?). Once properly put on and heat-shrunk, they are pretty good. However, the connector barrels are too short for my liking, allowing only a single
crimp. Also, you tend to spoil a few putting them on because the special crimper tends to slip as you execute the crimp. It slips up or down the barrel, sometimes even when you try to anticipate the slip and hold it tightly.
More in frustration than anything else, and with a sense of professional pride, I tend to use heavy adhesive-lined heat shrink tubing over BOTH types of connectors (yes, heat shrink over heat shrink in the case of the 3M terminals). This makes for a secure, water
resistant, and reliable connection no matter which ring terminals you use.