Different jobs, not head-to-head rivals
It is tempting to treat WeddingWire and Zola as direct competitors, but they are strongest at different jobs. WeddingWire, part of The Knot Worldwide, is a vendor-marketplace-and-reviews platform. Its center of gravity is helping couples find and vet photographers, planners, florists, caterers, and venues, with one of the largest review databases in the U.S. The free website builder is a useful add-on rather than the main event.
Zola is a registry-first platform. Its owned cash-fund and universal-retail registry is the best in the category, and its website builder is cleaner and more modern than WeddingWire's. Zola's vendor marketplace exists but is much smaller.