Now that I've had a bit more time to research both options thoroughly (And really, THANK YOU: I pretty much thought the Phantom 530/630 was the only option for me, until I came across this thread - I now know better, and I have more food for thought for my own build which is being done)...
Edit: I really need to stop with the verbal diarrhea. Better grab a tea and biscuit folks!
The way I see it:
NZXT Phantom 630:
Pro/Con:
Marmite look (either you like it or you don't)
No option for external radiators
Pros:
- 630: Two version: small window and large window, giving choice to consumer
- Cheaper case (where I am by ~$40-$60 depending on version you are looking at)
- Uniform front panel, unmarred by use of 5.25 bays even if you DO use them (courtesy of a door)
- Drive cage customisation
- Water cooling friendly (Only BIG question mark is; can a 60mm thick rad fit in the roof? Answer is subjective based on Mother board size/heat sink size)
- Due to the fans included, is one of the better performing air cooling based cases going around
- Coloured case options (White, Gunmetal, Black)
- Internal fan combination options
- Cable management is a breeze - can even run tubing down the back if you want.
- Back panel I/O light
Cons:
- Plasticy
- Drive trays are flimsy, and pretty unreliable esp. in transit
- Removal of drive trays, and using a rad in the front is of questionable benefit due to the shape of the front shroud
- Is the larger of the two cases
- Questionable state of whether a 60mm thick rad can fit in the roof can be a problem for some
- Not all cable management holes are grommetted
Obsidian 750D
Pros/Cons
"Classic" look, which some love, some don't
The number and size of the included fans may or may not be to your tastes
Window may or may not be to your tastes
Pros:
- DEFINITELY enough room for a 60mm thick radiator with fans attached in the roof
- Otherwise to the first point, similar watercooling options to the Phantom 630
- Is a more compact case, and so can fit where the Phantom may not
- Customisable drive set ups (not as many options as with the Phantom however)
- Cable management is relatively straight forward
- Has option for External Radiators, but is blocked off with steel, not grommets.
- Really NICE placement for SSD's (IMO better than the Phantom)
- More solid drive plates (i.e. not flimsy)
Cons:
- Top "filter"is not really a filter
- No clips on the trays (I mean, really, this is a feature of the family! Why not have it?)
- Usage of any of the 5.25"bays can disturb the look of the front panel, and there is no front door to make it "uniform"
- Is the more expensive case
- The case seems to be a MAGNET for fingerprints and skin marks. Upkeep of this case may not be a simple matter (unless this doesn't matter to you)
- With stock fans is a worse performer for air cooling
- E-ATX board support: no stand offs for you, but the grommets have been moved to allow it - this screams to me of "we couldn't afford to support it properly, so we'll half ass it"
So, before I started looking at these cases side by side like this, I was very much in the Phantom 630 camp, only because it is the one I had heard of, and researched quite thoroughly in my quest for a case which suits my look and my needs.
Has the list above changed my mind? Well, i'm not really sure. It's given me personally something to really go away and think about. The Obsidian, for me, is a very good fit; I like the classic look, and my space for my case is not unlimited, so a smaller chassis, with confirmed 60mm thick rad support in the roof is a serious boost to the Obsidians chances. But can I look past the cons for me (E-ATX, fingerprints, 5.25" bay spoiling looks, lack of clips on the side panel)?
At the time of this writing, I don't think that I will go for the Obsidian. The cons are just too many for me compared to the Phantom. Perhaps with further thought, this will change.
Not trying to hi-jack the thread OP - more trying to show you where I am coming from with a similar question, and highlighting my own thoughts accordingly. Hopefully, they will help you in your decision making process.