Ah, I have used both, but I also haven't been using OS X for the past couple years. One of them, I didn't remember which, was actually a PPC program that required a Rosetta to work. At some point it stopped working, and I switched to the other.

Since I hadn't used them in a while, I forgot which was which. However, some further research says that Disk Inventory X was the PPC program. In that case, I'd also recommend GrandPerspective.