Not speaking of intelligence.
I'm talking about gameplan.
Hingis always knew what she was doing out there. When asked about her attack-the-backhand strategy during her win over Serena in the 2001 AO quarterfinals, for example, Hingis said "I can't be stupid and hit to her forehand."
Hingis is now retired, of course, but what players do you think are the more intelligent ones on the court?
Zvonareva is always changing her gameplan.
Davenport is always aware of what she has to do... just a matter of execution.
Henin, like Hingis, has a lot of variety, and she usually looks pretty sure of the way she plays matches (and she knows Clijsters' game inside-out).
I think the dumbest player is Kim Clijsters. The only match I've ever seen her try a different strategy was the passive Kim at YEC 2002 against Serena, which just barely worked in one match. Other than that however, the girl seems so lost out there sometimes. Same for Serena, actually.
Sometimes Mauresmo looks very clueless on the court, like she's saying "I have all this game but what am I supposed to do with it?"
...Don't touch me please...
I cannot stand the way you tease!