I have played all range of speeds and I must admit the three worlds that I had the most fun in (Emporion, Sinope, and Baris) were are all speed 1 or 2. Worlds that roll along at a slow boil maintain a good player base because most players are not eliminated in the first week and you typically find upwards of ten alliances that can be competitive. Of course, that was then, not sure even a slow world can field these numbers anymore. Also, it allows you to have a life outside of the game and I think a lot of players favor this.
These faster worlds, especially now with all of the insta buy and gold pretty much come down to two alliances and the player base is horribly thin because most are eliminated, discouraged, and dare I say "bullied" right out of the gate.