Active case has a silicon layer, then a spine that sits on top of it - so you get the thick silicon protection to cushion falls, and the hard spine to give it support, protect the corners, and make it easy to slip in and out of your pocket.
seidioonline.com
The rugged case takes the base layer of an Innocase (hard case), adds a silicon case over that, and a spine over that. It's like an Innocase and an active case. Basically, you can launch it from a rocket and it will be protected. It also has covers for the ports and camera so that they are water resiliant (not water proof). It adds considerable girth to the phone. With this combo, you can choose to use the Innocase for every day use, and add the Rugged case for when you are, I don't know, jack-hammering your driveway.
seidioonline.com
FWIW - I love the active case and feel like my phone is very protected. Only gripe - the volume and camera buttons are hard to find, and the camera button is nearly impossible to activate without shaking the camera (because you have to push so hard) and so you have to activate the shutter by pressing the on-screen icon. A bit of a pain, but not a deal-breaker for me.