The Stacker is somewhat of a different league than either of the two Antec cases. It's going to run you about $100 more I think. It's going to be a high quality case with great cooling, of course, but unless you're really going for an extreme configuration, I'm not sure you're going to get much benefit out of that extra money, compared to the P180 or 900. The Stacker is going to give you more space (it's just bigger) and better cooling with 6 120mm fans to the 180's 4.
I'm not really sure that the 900 is much of a better cooler than the 180, especially if you go for good aftermarket coolers on you chipsets. The separation of the lower HDs and the PS in the P180 is going to give you a thermal advantage on the 180 but the 200mm fan and the side exhaust is going to be a plus for the 900. I've never used the 900, but I'm going to guess that the cooling difference between the two cannot be more than a degree or two if set up well, probably in favor of the 900. The cost is noise, as the P180 is a much quieter case. So the real question is what you want to do: if you're going for a maximum overclock with extreme air cooling, noise be damned, the 900 is your case. If you're only planning a moderate overclock, the extra cooling the 900 could give you is not going to come into play and you'd probably be happier with the quieter 180. In terms of quality and capacity, they're both about equal, with the 180 giving you slightly more room.
Finally, there's look. If you want a case that says, "I PLAY GAMES!" the 900 is your baby. Side window, LEDs, etc. The 180 is much more subdued and is going to look more like a piece of furniture, which isn't necessarily bad depending on your setting.