I've been working with webinars for 9 years. I've used several platforms and the only one that has never let me down is InstantTeleseminar. We were using GoToWebinar for major events at the corporate level and had constant problems with people getting no sound, people getting kicked off, and our own computer locking up. I told the company about InstantTeleseminar and we were off to the races. No more headaches.
It has powerpoint capability, chat rooms, and can be embedded into your own web page if you want to host from your own site, along with a lot of other great features.