GoToWebinar is one of the major webinar softwares in the space in terms of market share. Originally founded in 2006, it still maintains a lot of the same design elements that were used over 10 years ago.
GoToWebinar provides a webcast version of their software, but the majority of events are run with the standard downloaded version.
ON24 was built to be an engagement platform for prospects and customers in 1998. While the platform has been around for quite a while, it still maintains many of the outdated interface elements throughout the product; this results in a poor user and attendee experience. ON24 has a ton of great marketing features, but in many ways this also makes the application seem incredibly "busy" and hard to learn. It's far from a simple experience.
ON24 mainly targets Fortune 500 companies, and their prices are significantly higher than many platforms on the market. In order to even see their pricing, you'll need to get in touch with their sales team, as their pricing is not public.