The Sonata is a nice case, very well constructed and except for the placement of the front fan (behind the HDs rather than in front of them), well designed. But, what are you planning on putting in it? I put an Intel 560 in one a couple of months ago and it's been nothing but a cooling problem ever since. At this point I'm pulling the 560 out of the Sonata and putting it into a water cooled Lian-Li PC-V2100 that's leak testing as I type this. The Sonata is going to get an Intel 530 on an Asus P5GDC-V Deluxe, which with the slower chip and no video card (using the onboard video) should work well as a backup machine, though I am keeping my fingers crossed.
Bottom line, if you're going to be running older, or slower, hardware the Sonata is a nice quiet and well constructed case. If, however, you're going to be running one of the faster Prescotts or over clocking, or pushing the system at all, I'd stay away from it.
Oh, and as for a recommendation, if you're wanting to stay in the mid-tower size range, the new Lian-Li PC-V1100 is a very nice case, but any of it's "older" brethren would work well also.
The Sonata II is coming out soon, it was designed for much better airflow (among other things), doesn't have the big "ANTEC" cut into the side, and has a less restrictive front air intake grill thing.
SLK3700-BQE should be a good bargain case for the reasons noted. Add a second 120mm fan and I don't see how cooling could be an issue.