Goodness knows, there are a lot of highly regarded sets of The Well-Tempered Clavier to choose from; however, if you're looking for just one set my vote goes to this outstanding survey by Vladimir Feltsman. My points of reference for the WTC are Fischer and Richter, who take different approaches from each other and from Feltsman as well. Feltsman doesn't ruminate the way Richter often does, nor does he take off in manic spurts of speed the way Fisher sometimes does. Instead he focuses on structure while always finding the music in the notes. It's a joy to hear the pianist moving things forward, but never rushing, finding and expressing poetry and at the same time always mindful of the dance-like elements in the scores.
The two books of the WTC add up to a lot of notes, and even though I rarely listen to more than one book of preludes at a sitting this can still lead to listener fatigue after a while, something that I was especially susceptible to when playing Richter's recording. This is never the case with Feltsman. (By the way, there are four hours and forty of minutes of music spread over four discs in this set. While most sets of the WTC are issued on four discs, Ashkenazy's recent set on Decca has been compressed onto three discs, which in my view is a negative for listeners who would prefer not to have the books split unevenly between discs.)
Recorded in 1992 (Book 1) and 1995 (Book 2), and originally released by MusicMasters, this newly reissued set from Nimbus also benefits from high production standards. The set was produced and engineered by Max Wilcox, who produced nearly sixty of Artur Rubinstein's recordings for RCA, and it's no surprise that the musical results as well as the sound are superb.
Very highly recommended!