Contact Form 7 is the more common of the two in our index: it runs on 1,148 websites against 41 for PixelYourSite, and 12 sites use both. Counts come from real scans, not vendor claims.
Contact Form 7 is an WordPress plugin which can manage multiple contact forms. The form supports Ajax-powered submitting, CAPTCHA, Akismet spam filtering.
PixelyourSite is now probably the most complex tracking tool for WordPress, managing the Facebook Pixel, Google Analytics, Google Ads Remarketing, Pinterest Tag, Bing Tag, and virtually any other script.
12 sites run both Contact Form 7 and PixelYourSite. That is 29% of the sites using PixelYourSite, the smaller of the two.
Want to know which one a particular site uses? Look it up and see its whole stack, or compare two sites side by side.