The verdict
For a small B2B team that runs webinars and product demos, pick Demio. It is built for exactly that, the setup is quick, and the engagement data is useful to sales on day one.
If you run a real event programme, with several tracks, a mix of in-person and online guests and a need to prove results to the business, pick Webex Events. This is especially true if your company already runs on Webex or Cisco and wants one vendor.
I'd pick Demio for most readers of this site. Webex Events does not publish prices, so expect a sales conversation and a written quote. That is more platform and more process than a webinar needs.