Since John Newcombe's serve was generally ranked the best of his time I would rank Newk's serve higher than Tanner or Dibley. Dibley's serve was fast but he double faulted a lot and few if any ranked it higher than Newcombe. I would tend to rank Newcombe's serve better than Tanner's or Dibley's. Tanner's was awesome and with the fact that he seemed to almost hit his serve when the ball toss was still going up made the reaction time to the receiver much shorter. I'm glad the Tennis Channel has some Tanner matches available just to check out the serve.
Sampras' serve is particularly impressive considering how often he led the ATP in percentage of holding serve. I believe he led the ATP in that most important category most of the time in the 1990's and even in his worst years was in the top ten. Now I know it has a lot to do with his overall skills but still his serve was great. I saw an interview with Segura in which he ranked Sampras' second serve a bit higher than Jack Kramer's and Kramer's second serve was considered the best of his time, perhaps of all time. So that's a great comment by an expert who knows about tennis.
The Tilden first serve was excellent but I heard his second serve wasn't that impressive.
One serve that is not mentioned but perhaps at worst deserves an honorable mention is Ivan Lendl's serve. He had a very powerful first serve and an excellent second serve. I heard an interview years ago in New York that Brad Gilbert did. They asked him who had the toughest serve for him. He answered Ivan Lendl. The reason was that besides the fact his serve was so powerful, that he had such a variety of serves and every one of them were very good.