Tinychat is the only one of these that doesn't sound like baby talk. Skype has done well and become a verb ("Skype me") and I don't see anyone asking to voxox, oovoo, or goober me anytime soon. There is a big gap out there for someone to offer a good quality, serious competitor.
Maybe. Do you (or anyone else) have a preference?
For webcaming, I've personally found ooVoo to have better quality than Skype.
I tried ooVoo recently as my significant other had problems getting Skype working. I must say I can't see it as a competitor to Skype. The UI is borderline unusable due to all the flashing ads. What's worse is my contact list of one got deleted, and it was impossible to re-add my GF. That was on day 2. A few days later, she was back on my contact list. I don't trust it, and it's a pain to use due to all the ads and the general UI.
Goober is the only one with a Linux client. I may have to try that one out.