I’ve been using Tailscale because I like the business model they’ve been pushing. They’ve also followed through with that, expanding what the free tier of their service offers instead of restricting it more.
Although possibly biased, Tailscale has a write up comparing the two and the conclusion is that both are good at accomplishing their goals. If you have a technology or business preference, it could mostly come down to that. tailscale.com/compare/zerotier/