Both are excellant cases, the Phantom is brilliant, i have used a few for builds and i really like them.
Like you said the HAF has an big following, and is easier to mod, as its been around a while is is a great starting point.
If you prefer the NZXT then go for it, you wont regret buying it.
The rest of the build looks sweet, although if you can stretch the extra $30 to the 2TB barracuda its deffinately worth it. 2TB drives are the best value drives atm, but it'll soon be 3TB or more.