I have used Moodle and OpenHive (Sharepoint). Personally, I wouldn't say Edmodo is a VLE. Or at least, it isn't a whole school VLE. I use Edmodo as a classroom teacher and I think it is fantastic for that. It is easy to set, receive and mark homework and then to give feedback. It is easy to send and receive private messages to kids. It is quite good for class discussions however the facebook-like wall does limit this as things very easily get lost as they move too far down the page.
In terms of whole school, Edmodo just doesn't fit the bill. A whole school VLE needs some sort of centralised information area. This doesn't exist in Edmodo. You could implement it, I reckon, but it would be difficult, require a lot of organisation and I imagine would easily be forgotten about.
I use Edmodo to do the learning stuff along side our VLE. We have OpenHive which has no real functionality for learning (i.e. set work, receive work, mark work, give feedback, gradebooks, view progress) unless you use the Learning part of it which is silverlight based and is not well designed. Edmodo does the learning stuff really well, I think.