[T-Mobile Samsung Galaxy S II SGH-T989] a12m4nd0:
I have 6 cases for this phone (I don't know what I was thinking). It's nice to have the option to switch between the cases, especially because I own the white T989 but for me there's one I consistently go back to. I'll list pros/cons of the ones I have, in case it helps anyone. All cases have the ports open and mic holes exposed so I won't list that anywhere.

Fishbone (White plastic backing)

Price: $

Pros: Lightweight, thin, stylish, easy to put on and take off and easy to push the volume rocker and power buttons. All ports easily accessible and no mic holes are covered. Will protect against light drops and cosmetic phone injuries, like scratches.

Cons: The contrasting textures of the glossy plastic and the soft silicone bothered me. The silicone attracts a lot of lint and the two piece design is flawed in that it doesn't wrap around in the middle, leaving the silicone cover feeling very loose. It never really felt secure and this makes it lose a lot of points.

Diztronic TPU, 2nd Revision (Clear Matte)

Price: $

Pros: Lightweight, very thin, exposes the volume/power buttons (which is the best solution, in my opinion) and hugs the phone nicely while being easy to put on and take off. Feels wonderful in your hands and won't slide around. In my opinion, the best combination of thinness and protection. The opacity of the case allows the white to be shown.

Cons: It probably wouldn't protect against a major fall, though when I dropped mine onto a set of subway stairs, the phone survived with no damage whatsoever.

Trident Aegis (Blue Silicone)

Price: $$$

Pros:Best protection for the phone of all the cases I own, hands down. Dropped with no worries of damage whatsoever. The buttons are easy to press and the blue silicone stands out quite nicely. The higher quality silicone doesn't attract as much lint and the polycarbonate backing's texture makes it very easy to hold, with a nice feel. The ports have a covering to protect against lint, dirt and debris from entering.

Cons:The case is protective but very thick. If you care about preserving the thinness of the phone, this isn't for you. I felt like I was holding a Game Boy at times. The case also completely covered the phone, so I missed out on the white. It is also quite difficult to take off and put on, as the polycarbonate backing is stiff and takes time to finally go over the silicone. Definitely going to annoy the hell out of you if you happen to do a lot of battery pulls.

Seidio Active w/ Kickstand (Amethyst)

Price:$$$

Pros: Great combination of protection and thinness; your phone will feel tight and secure in your hand. The color is neat. Similar in design to the Fishbone case in how it works (silicone and polycarbonate backing) but much improved, especially when it comes to keeping the silicone wrapped around the entire bezel of the phone. Buttons are covered but easy to press. Includes a kickstand if you like that sort of thing, but I found myself using it very rarely.

Cons: Many people complain about the design resembling a grenade, but that's an aesthetic preference that varies with color. Silicone isn't as high in quality as the Aegis, so lint is a problem. The kickstand hinge feels like it's going to snap off EVERY time I click it open or closed, which is probably what makes me paranoid about using it.

D30 Flex case (Blue)

Price: $$

Pros: The D30 is protective and I felt like my phone was safe within the case. The blue case with the white phone looked nice together and the thinness was pretty good.

Cons: For the love of Jesus, the buttons are SO DAMN DIFFICULT to press! I'm aware that there are modifications one can perform to facilitate that, but I prefer to use a case as it was intended. You really have to push, especially for that power button. It was a HUGE turn off for me. The case can also, depending how it fits, lift up your screen protectors edges which can really screw it up and trap dirt or lint beneath it. The case was also not as snug as I would have liked and I was a bit worried that the phone could come out if the drop was bad enough.

Wireless Central Brand Hybrid Plastic/TPU case (Clear/Black)

Price: $$$

Pros: Meant to mimic a band case. Easy to remove and put on. The plastic backing is completely clear and displays the white battery cover, which compliments the black TPU. Aesthetically pleasing and not too thick.

Cons: The plastic on the back, where your phone is likely to rest when you put it down, is slippery and can slide around. There will also always be a bit of a space between the plastic and the back of your phone. Might help with shock absorption but it annoyed me because it allowed particles to get stuck there, which then become very visible.

In my opinion, the best case (and the one I always tend to go back to) is the Diztronic TPU, followed by the Seidio Active. I switch between them most frequently. The Diztronic almost feels like you don't have a case on and pretty much enhances the phone's natural state while offering adequate protection. For the price, it's the best. In last would definitely be the D30. Hopefully the cases for future phones from them aren't so stiff and fit better. Then again, this is all subjective and your mileage may vary.