i know a lot of folks like crowdcast.io. i have attended a bunch of webinars with folks using it and from a user perspective on my end as an attendee it is great. you sign up. you get email reminders. it is easy to add to your calendar. you can view a recorded replay at at anytime by just signing into your account.
also it is cool that you can queue up questions to be answered during the webinar and folks can jump to those answers when watching the replay. also if it is a webinar where folks get to submit questions … it is really easy to do so and there is an upvoting system. most webinars i have been on with questions involved will answer the questions in the order of the most up votes. also you can do polls.
you definitely should check it out.
the other platform i know folks use is webinarninja.co