The whole organization uses GoToMeeting. We use it to deliver live sessions to small groups of customers, and we use it for Sales calls with prospective customers. It provides us a conference bridge integrated with slide and screen sharing (live demo) capabilities.
Sometimes it still requires attendees to download even if they've just used GTM that morning.
Would love for GTM to interface with salesforce.com.
Would like to have the ability to go above the 26 person limit on an as-needed basis and just pay extra for the additional attendees. It's very rare that we go over 26, so it's not worth buying GoToWebinar or GoToTraining, but I hate to just block people in those rare circumstances.
All have nice features, and no single one seems to have everything, but I like GoToMeeting best because it is an industry standard that most people are familiar with and it works consistently even when some people connect by phone and others by VoIP.