I've ALWAYS had Otterbox cases for the phones I had cases for. This is my first Spigen case, I invested in theie Tough Armor case.
The Otterboxes were all rugged, and had this nice non-smooth finish. It made gripping the phone great, and make the potential of the phone sliding on an gently inclined surface virtually null. Long story short, I've always been happy.
The Spigen case, is smooth, but the rubber on the corners and top and bottom of the phone help it not slide too easily, but the metal-like back does make it slippery on some sides. The Spigen case is also smaller than the Otterbox.
Honestly, between the 2, the Otterbox feels like a more secure case, but it's because it feels like there's more material surrounding the phone, where as the Spigen simply has less. But in all, the difference doesn't feel huge. If you want protection with little regard to look; Otterbox. If you want protection but want it to look good; Spigen.