If you're bringing one or more individuals into a room to watch a presentation, or if you're having a virtual meeting I would recommend Skype or Skype for Business dependent on the number of people. Both are cost effective, though I believe only Skype for Business has a relatively firm guarantee when it comes to reliability.
From personal experience with the two I would recommend not running them via wifi. Dependent on your Ethernet hookup situation connectivity may or may not be an issue. I've also found it works best if you are able to conference call on the phone (for audio) and conference call on Skype (for video) simultaneously. This limits the load on the program and allows individuals with slower connections to still hear what's going on if the video has lag. Lastly, I do want to bring up that recently we had a problem with firewalls not allowing users to connect. We were able to resolve the issue, however I would recommend always testing connections with new people prior to using the program for a meeting.
This recommendation is based on personal experience, so I may not have used a service that works better for your purposes. Regardless, I hope this recommendation was somewhat helpful.
The researchers above have already listed some excellent choices. Nevertheless, if you are still looking for something different, I would suggest WebEx: