Corsair Carbide Air 540 if you want a great air cooled case. Obsidian series is not great for air cooling but is great for watercooling and looks.....
I absolutely
cannot recommend the Carbide Air 540. I've owned a few Corsair cases over the years (Obsidian 550D, Obsidian 800D, Obsidian 900D, Carbide Air 540), and while they've all had their own issues, the Air 540 is the only one that I loathed after using it. Now, I might be a bit more picky than some users, but there are a few things that I really cannot excuse:
1) This case is just way too expensive for what you get. The case has a $150 MSRP, and it tends to retail for about that much. So, what's the problem? I listed cases up above that cost even more! Well, the issue is that the case feels cheap and looks cheap. That makes sense once you realize that the case is about 50% plastic and 50% steel. Yes, it's constructed much like those cheap, bargain bin $40 white OEM cases. The 550D is a similarly priced case, and even though it also uses considerably more plastic than its pricier brethren (800D and 900D use considerably more aluminum), it looks far better.
2) There is a serious design flaw with the rear case fan. Now, I'm not talking about the idiotic choice to make a removable fan grill on the back (who does that?), but rather the fact that you cannot use most aftermarket fans in that spot. There are two problems that I encountered. The first is that if there's anything in between the space between the mounting holes (such as Corsair's rubber mounts on the AF and SP series fans), that will hit against a lip in the case, which means it cannot reach the mounting points. If you manage to get a fan that doesn't have anything in the way, it also cannot have a square shape! If your fan has a square shape, it will cover the side panel's screw hole, which means you can't screw in the side panel's top thumb screw.
3) There's a serious lack of airflow over the left 3.5" HDD, which caused it to have temperatures about 5C higher than the right drive. It probably also doesn't help that it's right below the video card.
4) The 2.5" drive carriage is built for 9.5mm drives, and anything smaller (e.g. Samsung 840 series SSDs) will wobble in the cage. Given the price tag, Corsair should have included some sort of cable or mechanism to provide power to these drives. The issue that I ran into is that they're all so close together, that it's rather awkward to plug in the power cables. To be fair, this is actually a problem on quite a lot of cases. You should see how much fun it is to use the drive bays on the bottom of the 900D!
Honestly, I think the Obsidian 550D is better than the Air 540, and the temperatures are only 1-3C higher. Of course, I did put a 140mm fan on the bottom (near the PSU) and a 120mm (a 140mm fan wouldn't fit) on the lower mount on the side panel. As you mentioned, Obsidian cases usually have sub-standard air flow, but those two fans really helped to alleviate that. Although, I think the 550D is too small. I would love to see a version of it that's about the size of the 800D.
Rosewill Thor V2. $130, save the rest for upgrading hardware. This thing moves a lot of air very quietly.
Hmm I'm not as much of a fan of the looks of that case, but I do like the abundance of air cooling options! Given how ridiculously overkill my 900D is for an air-cooled, single-GPU PC, I'm tempted to try it out.