For City of the Chasch and Servants of the Wankh I really like the DAW paperback covers by H. R. Van Dongen. They wonderfully capture the atmosphere of Vancian science fantasy. But for the following two books, The Dirdir and The Pnume,  I prefer the Mayflower paperbacks. 

I visualize the dirdir as extremely bizarre (or is that a genetically related variant of the dirdir? I don't remember.), and on the Daw paperback they look much too humanoid to me.

The Pnume Mayflower cover is one of my absolute favorites. It is a pretty good imitation of Hieronymus Bosch's style of painting. But what really grabs me is the delicious science fantasy setting. Look at the medieval time-line of the man fighting the dragonesque creature, ... and then in the background, behind the hill, rests a perfectly round, artificially constructed spaceship. That is the kind of contrast I love in science fantasy! Old fashioned and modern, past and future combined in the same scene!