ZOOM - easiest to use, as it does not require host to be present before attendants and if you set the invite as "recurring" you will be able to re-use the same link forever. However, there have been some security concerns with uninvited participants. Free account available, but calls with more than three participants time out after 40 minutes and require you to re-click on the same link to get back in. Requires app or extension download the first time you use it, but invitees don't need to create an account.
Skype - there's a new "Meet Now!" solution available that is more similar to Zoom and does not require one party to actively dial the other one, both can simply enter at the link with no sign-ups or downloads.
BlueJeans - similar to Zoom, occasionally even better video quality. But there is no free account
Google Hangouts - the host needs to be present before the invitees and everyone may need a Google account
Houseparty - the more fun video conferencing application