I'd recommend an alienware case. I never had to clean it so far, and it has like automatic dust filters. and their easy to clean out too.
Just one thing for alienware, if you buy an earlie model be prepared to get a propietary psu, and if its the newest model then you should have no problems. except finding one.
also be aware they are preety much made of plastic, so they can break so easily. Don;t expect them to last. Although mine has lasted over 5 years.
I am comparing my alienware to my old antec 900, on my antec 900 I had to clean it every 2 days, howerver I never used filters. I have never seen my alienware dusty, and its right next to the open window. So its great for that.