These tools all give you some sort of network control from the Desktop - a service traditionally provided by daemons and initialisation scripts. The problem with that is roaming - it's much more common nowadays to have a laptop travel between multiple access points (Ethernet, 802.11, wireless broadband...) and many of the tasks can be automated. So what better way to use a point-and-click approach.
The three competitors, and here's how they compare by features:
|Tool||802.11 (wireless) control||ethernet control||mobile broadband control||VPN control||dbus notification|
|wicd||yes||yes||no||planned for 2.0||no|
Personally I use NetworkManager. I use all types of network control, and the dbus notification tells my mail client to go offline as soon as the network in not available. (Previously I would have to wait for my mail client to time out).
This is not saying that you should use NetworkManager too - find the list of features you require and use the appropriate tool.
Be warned: NetworkManager, while feature rich, is polarising the community - either it works and you love it, or it doesn't work and you hate it. There is a common wireless connect-disconnect issue which seems to be caused by various different problems. I see it at work but not at home. According to one dev, it's buggy kernel drivers, but that doesn't explain why it works for me in some places but not others on the same laptop. YMMV!
*My development laptop provided by customer A is locked out of their domain - stupid windows! My employer only has the this job for me right now, so I have to wait until they resolve the problem...