Prices listed are directly from the manufacturers website, I am sure you could find them cheaper elsewhere.
This case isn't too thick but it is thicker than the AT&T Gel case and will offer more protection against drops. Incipio's NGP is a TPU style case, so it's more stiff than traditional silicone cases and it doesn't attract any lint. The fit is very tight and leaves all the ports open, and covers all the buttons.
The only issue I had with this case was that the buttons are a bit tough to press. Especially when taking photos because it's hard to press the camera button on it's first stage for focus, I found it was a bit frustrating when using this case and taking photos. Other than that it's a very nice TPU style case that isn't too expensive.
This is more of a silicone type case, it's very flexible and has a smooth feel and doesn't attract lint. All the ports are left open, the buttons are covered.
This case is awesome if you like the look and feel of a naked phone because you can hardly tell this case is on the phone. The buttons are very easy to press. It does offer some protection but not as much as the Incipio NGP. I really enjoyed this case due to the fact that it feels like there's no case on the phone at all. It's not too pricey at 20 bucks.
Case-Mate Tough Case
This case has an inner soft silicone piece and an outer polycarbonate shell that fits over the silicone. The shell also has a rubbery coating. This case is the thickest of the three, it is also the most protective against drops. I really like this case due to the protection it offers. It fits very well.
This case seems like something Otterbox would have made, it reminds me of their commuter series cases. It leaves all the ports open, it covers the buttons and they are easy to press. The one thing to note is the camera cutout is much small than the other two cases which I personally like, that means that little chrome strip in the back is less likely to get scratched up.
The silicone on this case does collect a bit of lint which is kind of annoying. It's a bit of a trade-off for the protection. It fits very well and looks good. It does thicken the phone up a good amount but that doesn't bother me personally.
Overall it's a very nice case, and the best choice if you want protection, a little more expensive than the others but you are getting something more protective.
[Unfortunately I don't have enough posts to add my link to all the photos I took... :(