CloudFlare Analytics vs. Other Services
Google Analytics and other web-based analytics programs track visitors that trigger JavaScript. As a result, threats, bots and automated crawlers are not recorded since these visitors typically do not trigger JavaScript. These services also don't track visitors who leave a page before it is fully loaded or have Javascript disabled. CloudFlare tracks all of your traffic by requests, so your CloudFlare visitor number is most likely higher.
Keep in mind: CloudFlare can only track visitors that go through the CloudFlare system, which is represented by an orange cloud on your DNS settings page.