Some cars do like to snap oversteer, and you don't want that. But, a nice, controlled oversteer is very nice to have.
Also, the course has to be considered. In a really tight course with multiple low-speed switchbacks you might want to err toward a slight understeer, as low speed oversteer gets really "choppy" at times. You nearly come to a stop to control it if it gets out just a tad too much. With sweeping corners I'd always prefer oversteer.