What I'm not to crazy about on the Thermaltake Urban R21 is the lack of any sort of holes/grommets for cable routing. They make the build look really clean in this pic, but notice that there are no cables hooked up to anything.
This looks like a case from about 5years ago IMO. I don't think I'd buy a case anymore that didn't have some sort of cable routing options.
As far as Corsair goes... Corsair has some really well thought out designs, but in their more recently released cases, I feel their build quality has slipped quite a bit. The metal parts are thin, and the plastic they use is brittle.
They have an older 600T next to a newer Air 540 at my local Fry's, and the difference in build quality is staggering. ...not to mention that most of plastic pieces on the newer 540 are broken.
That being said, you probably won't see as many issues with the simpler cases you are considering mainly because there are less little fiddly bits to break.
If possible, I strongly suggest visiting a Fry's, Micro Center, or any other place that has some cases on display. Getting to see and touch them will usually help make your decision easier.
I am sure that the reason for the lake of material and build quality is the outsourcing of these items to that far eastern country where things are quoted so cheap, that they have to use cheap materials, and slap them together, in order to make any money on the end product. It is a very sad thing when a good design has to suffer from cheap emplimentation.
I have been looking at the Cooler Master N600, and am curious if their cases are made here in the states or in the far east.
Sadly, I don't have any large computer equipment stores in my area, only small Mom and Pop cumputer builders and repair shops. That said, I am going to one of these this Saturday, to look at the one black mid tower case that they have to offer.