We subjected Defender Series to our grueling OtterBox Certified Drop+ Protection program, running it through a battery of 24+ tests over 238+ hours. Drop Tests, Abrasion Tests, Thermal Shock Tests, UV Tests. When the dust settled, the data said conclusively: Defender Series is a survivor.
I have the Candyshell with the Otterbox Defender on its way. The Candyshell is pretty good in terms of protection. It's probably a little thicker than most of the silicone/slim cases out there but nothing I would call overly bulky. Overall it's a great case however taking the phone in/out of the Candyshell can be quite a pain.
Speck MightyShell: when durability is your main concern. The Speck MightyShell is Speck’s best technology in one case; this is the head honcho of protection out of what Speck has to offer. With double the protection of the military (MIL-STD-810G) drop test standard, this case provides excellent protection from dropping, crushing, and bumping.
The Spigen Tough Armor does not have a screen protector built-in. I'm not a fan of the iPhone 6 Plus case I just received. I did receive an Otterbox for the iPhone 6 and it seems to be an improvement over the previous generations. Of course, a lot of people have issues with the Otterbox scratching the phones.