Been using for a while both Seidio´s Active and Surface cases (with its holster) and I have to say these are the best in its class. For really good protection (Active) and for the heavy duty activities of the day and the Surface, providing lightness and also a good protective standard. Both very stylish, by the way.
Otterbox are, for me, to bulky while the Active from Seidio does the same job perfectly, without that bulk.
However, if like me, you use the HD or Standard Dock and the Lapdock, get the Trident Aegis case, such a fantastic design that allows your Atrix to connect to these docks without removing the case (due to design only have to flip the back part cover) and yet, achieve a high level in protection. Also, this design allows you to have a built in stand for your Atrix. However, this won´t fit the Car Dock.
And if you want full conectivity with docks, including car dock, better look for the Incipio Feather or the BlackFrost Case from Cygnett, both allowing full conectivity providing you take the little flaps out from any dock.
Hope to help, good luck!