Primal is quicker to setup for zaps if you use the built-in wallet (referring to the apps, not the web version), which is how I assume most people will use it. Damus requires using an external wallet. Zaps in Damus are also officially only profile zaps, although there is a script you can run to enable zaps on individual notes. I assume they'll have note zaps when they launch Damus Android though, since it was only removed due to Apple's restrictions.