Looking for a good nav plugin

I was curious if anyone had a good recommendation for a responsive menu for WPMU with a developer license?

In our custom development it would be nice to have a solid menu that is developed well and not likely to fade away.

We really like http://wpmegamenu.com/ but this menu has to be acquired one license at a time.

Characteristics we would like:

Responsive

Multiple style

Horizontal and vertical options

Ability to insert bg images for buttons or add images.

Mega Menu

Any recommendations are appreciated. Flexibility is huge. For Joomla we use swmenupro.