I bought the HAF X about three years ago for my new system because I wanted something that could be well ventilated by quiet fans. The quietest, and I would say the best, fans for this job are of course 200 mm fans for the role of feeding ambient air into the case.
The 200 mm fans draw in a lot of cooler air but unlike smaller fans will not act like a vacuum cleaner and thus will not clog up the mesh filter as quickly.
I have recently built up a NAS box and given my overwhelmingly positive experience with the HAF X I looked at it and the HAF XM.
I would say now, having bought the HAF XM and having experience with it, if I had had the choice between the two of them three years ago I would have gone with the HAF XM.
I have added another two 200 mm fans to the chassis (one in the side to suck air in and another at the top to exhaust the air) and it is nigh on silent.
Sure there are better cases that I would choose, however those cases are over twice the price of the HAF XM (or HAF X) and only marginally better in my estimation.
I want a case that gets the job done and not one to be seen posing beside, so I don't give a toss about "looks great". What's the point in having an amazing looking case that consigns the components inside to a premature heat death? However given that, I like the aesthetics of the HAF X and the HAF XM so I didn't really need to compromise on that score either.
CoolerMaster HAF X, i7-990x, Gigabyte X58A-UD3R, 24GB Corsair XMS, Sapphire 7950 Vapor-X, Corsair Neutron 128GB, 3*Seagate HD (3TB), Seagate HD (1.5TB), Hitachi HD (2TB), Plextor DVD + BluRay, StorageWorks DAT 72, 29160 SCSI Adapter, Corsair H80