Bloody hell, what an interesting question.
Both are similiar in features, personally I would go for the cheaper of the two. I think the Corsair may do a better job of keeping out the dust, but maybe at the minor expense of temps. But until stock is available there is no definite answer.
Mind you, there is no info on the Corsair pricing yet. I have put the HAF X up as I have obtained pricing, however no ETA for the HAF, the Corsair I have no pricing, but an ETA of August for stock.
20/20 LOL
Gut instinct and experience with Corsair casing I would realistically expect the HAF X to be cheaper of the two.