I'm using Black & Whitelist. Now at this time, I don't need a call blocker/rejector for any specific caller/spammer. However, if I find that I have a need in the future, I'll be ready. I do like that Black & Whitelist recognizes and supports unknown callers and callers with blocked numbers, in addition to punting callers that are specified in a Blacklist, and that the blacklist can be turned off without removing the callers from the list.

I tested it in a variety of circumstances and am satisfied that it will do what I want when the time comes that I'd need it.