Each tools has their advantages and limitations when it comes to working with teams online. While MSN's Service is not longer available, Skype and Google Hangouts have a very similar basic function of providing the opportunity for users to view each other and have a video conference meeting through the web. Users typically can still text and send links or files through the chat function and the focus is primarily on the user.
Skype does also have the function of sharing screens however so that if I am meeting with someone who needs help accessing a feature in a program or I am presenting a slide deck presentation, this works as a nice way to switch from the presenter to the content and then back to the presenter during the Q&A afterwards.
In tools such as Join.me or WebEx the focus is primarily on the desktop and not the presenter. Voice is shared for meeting purposes, however the focus is typically on the presenter's desktop unless they have assigned presenting rights over to another user.
An advantage of Join.me is that one can relinquish control of the cursor to another user. With that feature one can use it to let someone who is remote edit a file that it on their desktop. Or help trouble shoot a technical problem at a distance.
Blackboard Collaborate however offers the ability to group users into teams, and have private break out sessions after having worked in the main environment. There is a whiteboard for drawing or writing collaboratively, as well as a feature that allows the presenter to take users to a specific website and individuals can proceed by interacting with the presented site. You can poll your users, and questions can be queued up using a feature much like the classroom where they raise their hand.
Blackboard and WebEx are proprietary software and require licencing or membership to use. The other options are excellent resources and while they do require an account, they tend to be free and the results are just as good so long as you do not require the group/breakout room function found only in Bb Collaborate.