They both look really nice... I have the Thermaltake Tsunami and this is the happiest I have ever been owning a case which did not need modding...
I have no experience with that Thermaltake case, but they do make a good product, and the thing I like is that you have the audio port on the side; but it depends on where the CPU is sitting vs where you are sitting in my case the tsunami sits to my right, so its audio being on top just "fits" better...
Coolermaster has some nice cases as well... anyone who has a coolermaster chime in with ideas for him thanks!
I use the tsunami myself and while i like the looks and such I was severly dissapointed when building it. They tried to create a toolless case and ended up creating a headache. The snap pieces for the PCI-E/PCI cards were junk so I ended up screwing those in anyways, I was trying to mount a fan spare 5.25" bay but couldn't because the arms were only long enough to fit one screw in and the tsunami doesn't allow you to screw in 5.25" drives, instead they force you to use their rails (there are no screw holes in the case for these drives) and the rails don't screw on either instead they have little pegs that just slip into the holes on the drive. In short for a PC enthusiast case I was severly dissapointed by the lack of ability to customize it they may have improved on their cases by now though. On the other hand although I have never had one I have heard nothing but Good things regarding the Gigabyte cases (designed by coolermaster right?). One thing I like about the Coolermaster cases, assumingly the gigabyte are the same, is mounting the HDD sideways, makes access so much easier. Anyways just my $.02.
I love my Sonata too. Its beauty is in its simplicity.
I looked at a number of different cases back when I was building my machine, and didn't like even the more expensive ones because they felt too elaborate and over-designed.
The only case that caught my eye from the ones posted here is that black CM Mystique 632 that Mecham mentioned. I'd probably pick up one of those if I was building something now. The Antec P180/180B is pretty nice too.