I have been to a number of seminars (Drysdale, Comprido, Traven, Felipe Costa, Francisco Mansor) who do you feel puts on the greatest seminar and why? 
Xande. Simple yet effective. Concepts of pressure and space you will use forever
relson.. man the stories.
Tony Pacenski does great seminars. I've been to a few, and I always walk away with really useful information.
jakem - relson.. man the stories..
I have been to a few different ones. The ones I liked the best took a holistic approach to BJJ helping me connect the dots and right away improved my training.
Saulo Ribeiro not only provided amazing technical details, but had a coherent unifying philosophy behind what he shows, and also provides tips on the mind set and overall strategy he employing form the positions he shows.
Xande Ribeiro for the reasons checkuroil listed above.
Royler Gracie self defense based seminar, had people grinning two days later.
Those are my top 3
I have heard form those who have attended Rickson's seminars that they are worth every penny.
Mendes Bros
Kashk - I have been to a few different ones. The ones I liked the best took a holistic approach to BJJ helping me connect the dots and right away improved my training.
Saulo Ribeiro not only provided amazing technical details, but had a coherent unifying philosophy behind what he shows, and also provides tips on the mind set and overall strategy he employing form the positions he shows.
Xande Ribeiro for the reasons checkuroil listed above.
Royler Gracie self defense based seminar, had people grinning two days later.
Those are my top 3
I have heard form those who have attended Rickson's seminars that they are worth every penny.
Royler Gracie???
THE WORST period.
mbalz izhairy -Kashk - I have been to a few different ones. The ones I liked the best took a holistic approach to BJJ helping me connect the dots and right away improved my training.
Saulo Ribeiro not only provided amazing technical details, but had a coherent unifying philosophy behind what he shows, and also provides tips on the mind set and overall strategy he employing form the positions he shows.
Xande Ribeiro for the reasons checkuroil listed above.
Royler Gracie self defense based seminar, had people grinning two days later.
Those are my top 3
I have heard form those who have attended Rickson's seminars that they are worth every penny.
Royler Gracie???
THE WORST period.
U can't just post that without details. In. 
I went to a Dave and Dan Camarillo seminar last year and still use most of the techniques they showed. Great stuff!
Bruno Frazzato had one of the best seminars I have ever attended. He went into detail on things like berimbolos and 50/50 from double guard pull. And this was at a time when berimbolo was not well known yet and I didn't even know it as the "berimbolo." he didn't hold anything back and was clear and detailed. All that and the seminar was $40 for 3 hours.
I hear everyone say Relson has good seminars because of his stories. I'm sorry but when I go to a seminar, I don't think I want to hear the guy tell stories, I want the guy to show good jiujitsu. I don't understand how people can be satisfied with that
Terere - small details changed my whole outlook on positions
Telles - very very good, not just Turtle but his guard passing and half guard were amazing
Mike Fowler - biggest impact on my gameplan and teaching, learning structure.
Ryan Hall
skilgannon - Bruno Frazzato had one of the best seminars I have ever attended. He went into detail on things like berimbolos and 50/50 from double guard pull. And this was at a time when berimbolo was not well known yet and I didn't even know it as the "berimbolo." he didn't hold anything back and was clear and detailed. All that and the seminar was $40 for 3 hours.
I hear everyone say Relson has good seminars because of his stories. I'm sorry but when I go to a seminar, I don't think I want to hear the guy tell stories, I want the guy to show good jiujitsu. I don't understand how people can be satisfied with that
Good JiuJitsu = Great
Good JiuJitsu + Good Stories = Awesome
Also paying only $40 for a seminar is pretty awesome too !!
Rener , I use some of the stuff he taught in almost every roll, or atleast I try too.
I went to one Royler seminar. He showed a lot of Self Defense technique's as does Rickson. Royler spent 2 hours on self defense and 30 minutes on one submission from side control BOTTOM then was q and a everyone gotta a lot of of best defense is NO get caught in a triangle. I actually purchased his DVD's and asked him a question regarding his wheel pass and he say " Ahhh didn't I answer that for you last time?"
I value a seminar by the % of techniques that can be applied immediately to my game.
With that in mind, the best seminars I've attended were by far John Danaher and Roger. The simplicity of the techniques and the universality of the principles applied are things that anyone can implement instantly and it's stuff that will last them their bjj career.
Second would be Braulio and Kyra, who also added little details to basic techniques that can take their success % through the roof.
I agree with ElFeroz about Royler seminar - one of the worst I've done by far.
The UG's own Delicious Bass gave a back seminar that changed my entire back game in one day.
I used to almost never go to the back, and when I did I'd bail to mount or side. I had trouble getting back, keeping back and certainly finishing from back.
Less than a month after that seminar, I was using his stuff in a competition like it had been part of my game for years.
Worst seminar was (sorry) Eddie Bravo in Montreal. 3 hours, of which one was spent fielding questions on BJ v St. Pierre from fanboys. I love some of Eddie's stuff and have great respect for his game, but that seminar went off the rails.
Also, how do you go to a seminar with tonnes of new people, and no one (absolutely no one) wants to roll after? I see a new guy with a bit of level, and I'm like a kid in a candy store (no homo), but everyone packed up and left right after the seminar was over. Lame.
Gui Mendes did a seminar at my school that from just 2 days put my game on a different level. I know a lot of my teammates feel the same. I can't imagine what it must be like to train with him and Rafa full time.