I would guess that ExpressVPN has had more third-party audits than any other VPN. According to their blog, as of November 9, 2022, they had completed a total of 11 such audits of various aspects of their service. And they have continued with multiple audits since then. I've never seen another VPN claim anywhere close to that level of external auditing. It speaks well to ExpressVPN's commitment to delivering a quality product that works as advertised.