I only have the Speck Candyshell Grip and love it. It add some bulk and weight, but much less than I expected. The case feels very sturdy to me. The main reason I love this case is the grip on this thing. And when the baby sees me using the phone and wants to play with it, I turn off the screen and let him hold it and even drop it with no fear of the phone breaking (but keeping an eye on him hoping he won't drop the phone screen first on a corner).
I don't have the Spigen you mentioned. But for comparison of another "tough case", I have a Ringke Max which is slimmer and lighter than the Candyshell Grip. Because of that...I'm not sure how well that one would protect against drops. The main reason I stopped using that one was the back is too slick and I feel like I'm going to drop the phone all the time.