Depending on your areas you fish, it will either be the navionics platinum or the Nav+. The platinum has 3d and overlay capabilities but is a regional card. The Nav+ does not have 3d or overlay but is a fully custom card as you draw boxes around the lakes you fish. Both have the sonarchart layer, so really up to you and your style of fishing.
You can view the mapping available in your areas by checking out the webapp at Navionics.com. It is updated daily.
In order to see the sonar charts layer and the differences it can make, you can toggle the button in the bottom left corner.
If you have any more questions, feel free to ask away.
Edited by Corey Stanley (02/24/16 10:54 AM)