Mmm good topic, I love a good dirty talker. I'm only referencing English here.

If we're talking WL, then no one beats Paula at No5. "I make you cum 25 times, until they take you away in an ambulance! Now give me that cock!"

ML is a different story, it's not as easy to find a good dirty talker. My top picks would be Anna @ St Peters or Kiki and Coco at 200 Stanmore. There are a couple of great dirty talkers who've unfortunately left the industry.