I looked seriously at all three cases before finally deciding on the P180. Although you said to ignore costs there is a blue version of the Stacker available for around $100 which is a LOT cheaper than the black/silver versions. Same case, just a different color. Try SVC.com to see if they are still running the deal. Another retailer had it also but I can't remember which one. The 900 has been dropping in price every week and is now close to $100 also. And Fry's has been running some fantastic pricing on the P180.
OK, the Stacker is out for me because of its size. It is immense. It's depth is 24" and the width is 9". Next to it the 900 looks like something that shrunk. The Stacker is really more for people into serious modding. One thing I noticed is that in order to get a second fan in the front you have to buy an entire HD cage. Or else, zip tie it to the frame which looks really tacky. I like seeing my case on the desktop next to me but this thing was just too extreme even if I really liked the blue color.
The 900 is a nice case even though a lot of people slammed it when it came out. I personally like its looks and have no problem with the little holder on the top. And the monster fan on the top looks pretty dramatic also. What killed the case for me was playing around with one and finding out what a major pain it is dealing with the placement of your hard drives. You must remove both side panels, then remove 8 thumbscrews, pull out the cage through the front, which means disconnecting all your HDs from the power supply and MB, and then screw in the actual drives. No rails here. If you plan on installing the drives and leaving them alone then I really liked the case. And the side window means you can play around with lighting which is also something I like to see. The case is fairly light but the side panels, especially the one with the window, are pretty flexible. I have read some user reviews who complained about have problems with extra long video cards. And there is/was a problem if your video card uses the top slot on the case. It will not correctly fit and you will not be able to connect your monitor. Antec is claiming to be fixing that with a new design and it only affected a few MBs anyway.
The P180 is a very solid looking and feeling case. The various compartments make it cramped and wiring it is a real pain if you want it to look neat. The bottom fan between the power supply mounting and the lower hard drive cage is a fat one. PSs that are extra long (more than 5") will mean you have to remove the fan. Some users have no problem with that. There are two HD cages so if you only have 1/2 HDs you can easily put them in the top cage on rails and not hassle so much with finding the right sized PS. The bottom HD cage will hold 4 HDs and they must each be screwed in. Since the cage is removed by pulling it towards you you don't have the hassles of the 900. And each HD, and the PS, are mounted on rubber for reducing vibration/sound. The upper cage will allow for a extra fan to be placed in front of it against the front of the case or you can skip using it for HDs and place a fan on the back side which will blow directly across the center of your MB. On the downside, I miss the light shows.
To be honest, I could live with any of these cases as long as the Stacker was the blue one. I still think the 900 is the neatest looking and I would have bought it except for the hassles with the placement of the HDs. Antec took a step forward and one backward with the case. Finally, the P180 is one of the most popular cases of all times which speaks for itself. Good luck.