My personal favorites, they are mostly watercooling optimized, but they look good either way:
-Corsair 900D ($260): this is my personal favourite case right now, and will house my next computer, its massive, beautifully built, relatively mod friendly (not too much though), and looks gorgeous.
-Phanteks Ethoo Primo ($270): perfect for watercooling one of the best built cases ever
-NZXT Phantom 820 ($260): best for air, fancy colour changing lights and unique design, however it has no basement
-Corsair Air 540 ($150) : cheaper, but still awesome, has 2 separate compartments, so ugly stuff like hard drives and PSU is hidden behind the motherboard tray)
-Silverstone TJ-11 ($600): this one is REALLY expensive, but in my opinion the best case ever. It has a 90 degree rotated motherboard, probably the most mod friendly case short of Caselabs, huge expandability.
And may I ask what you intend to put in it?
I have a serious problem with the Cosmos II. Its massive, and not massive like the TJ-11, its unnecessarily massive. It weighs a ton, and doesnt support enough hardware to justify its size (and cost). It is very well built, mind you. And can take a hit and protect whats inside, if that counts for anything. Out of your choices, I would pick the 900D, hands down. The Level 10 GT, I find to be less elegant, and in my opinion, almost childish. Again, it doesnt really justify its cost/size. That being said, I prefer simple cases, with subtly lighting rather than one that, to quote Corsair, "looks like its going to transform into a giant robot". But if thats what you like than go for it. I think the 820 is a good balance between the subtlety of the 900D and the sharp, unique design of the GT. Anyways, hope you have fun with your build.