It totally depends on what you care about the most. I've used pretty much every platform out there–if peace of mind is your top concern, go with ReadyTalk. They take the stress away with excellent customer service and a dedicated rep to sit in on your call. But if you want engagement metrics (who clicks away) and cleaner sound, GoToWebinar might be better. Their UI and customer service leave something to be desired. For a roundtable where you don't need in-depth tracking, use Google Hangouts. I'd be happy to talk more about all the options out there.