In terms of commercial success, AC/DC has the edge over Kiss. The band has sold more albums worldwide and has had more number-one singles on the Billboard Hot 100 chart. AC/DC has also been nominated for more Grammy Awards and has won more than Kiss.
However, Kiss has a larger fan base than AC/DC. The band's live shows are legendary and they have a very loyal following. Kiss is also more popular in some parts of the world, such as Europe and Asia.
Ultimately, it is difficult to say definitively which band is "bigger." Both AC/DC and Kiss are incredibly successful and have made a significant impact on the history of rock music.