Claudio Luis Vera has authored a very good comparison of the accessibility of different video-conferencing tools. A little heavy on survey responses at the open, which in matters like this I’m always a little skeptical of. There’s an undeniable brand-name/brand-recognition factor there, to some degree.
Beyond that, the article is filled with good advice, including this bit:
If you’re the one deciding which video conferencing platform to use in your organization, the lack of formal studies and the constant change will pose challenges. One good way to gauge a company’s commitment to accessibility is to look for an accessibility page on their website. Usually, it’s posted as a link in the footer of every page. A company that is at least aware of accessibility will have a posted accessibility policy.