It is benchmarked here against WebP, HEVC, and JPEG2000, as well as JPEG. That's what all the graphs are. AVIF wins quite convincingly on the metrics they've used.
Or indeed HEIC.
A lot of so-called "next generation" codecs are really "current-generation" now.
Benchmarks against HEVC and WebP are included in the metrics section of the article.
Does any browser support HEIC yet? To my knowledge, even Safari doesn't.