After much research, I've narrowed down my three choices to Smith Publicity, Black Chateau, and BooksForward. They each have different prospective author engagement procedures.

Smith is the most flexible, customizable option with large amounts of author resources for anyone to read at no charge on their website. I learned of them via Bookbaby, my printer and audiobook producer.

Black Chateau is the most transparent of the three with their four service tiers, with about 15 well-defined add-on packages. You know exactly what you'll get, how much it will cost, and on what timeframe. I value that clarity.

BooksForward is the smallest of the firms. They appear to be the firm most likely to connect in a direct manner, with the aim of really understanding, in an almost personal way, what drives their clients to write and publish. They even asked to read five chapters in order to assess the opportunity!

 I completed each firm's initial intake paperwork for new clients, and I await their responses.