According to Celebrity Net Worth, Gwen Stefani is worth $150 million and Blake Shelton is worth $60 million. So, Gwen Stefani is richer than Blake Shelton by $90 million.
Gwen Stefani made her fortune as the frontwoman of No Doubt, as well as through her successful solo career and various business ventures. Her estimated annual earnings are $17 million.
Blake Shelton has earned his fortune through his successful country music career, which includes hit songs, album sales, and touring revenue. His estimated annual earnings are $13.5 million.
In addition to their respective music careers, both Gwen Stefani and Blake Shelton have also appeared on television shows like The Voice (Gwen was a judge from 2014-2015 while Blake has been a judge since 2011). It's estimated that Gwen earned $8 million for her time on The Voice while Blake reportedly earns $13 million per season.
So overall, Gwen Stefani is richer than Blake Shelton thanks to her greater success in both the music industry and in other business ventures.