Best hand down is Skype as Skype have increased 10 limit of video conference up to 25 people video conference! Google Hangouts would be second best but for a lot smaller group as it can only allow 10 people video conference.
OoVoo can only bring 12 people to the video conference and has less features than both Skype and Google Hangouts. I never liked ooVoo as it don't bring what Skype has (up to 25 people video conference w/ file sharing, live chat, map, etc) and same goes for Google Hangouts (a few less features than Skype but definitely deserve a 2nd place and can bring in 10). Both Skype and Google Hangouts is a whole more popular than ooVoo is so there is a very high chance that your friends or family has account with Skype if not then Google Hangout and not everybody heard of ooVoo so I'd be surprised if some of your family or friends know about ooVoo as it doesn't reach the level that Skype is at or secondly Google Hangouts.