I've been to the Glen Ivy spa in Corona and in the Brea Mall. If you're looking for a fun day spent in the mud and other various hot springs with tons of other people, then Corona is your place. However, don't go expecting tons of amenities in the women's lounge or a relaxing "spa day." It was really crowded and seemed a little unkempt.
The Brea Mall has a much more crisp atmosphere and more amenities. The staff is attentive and keep all the areas looking clean and well stocked. I've had two massages in the past year, and they may be the last. My masseuse was a little weak on both occasions. I'd be willing to try other services due to their convenient location and relaxing atmosphere, but I was a little disappointed in the quality of massage service.