Not an easy one to answer, they are both good in their own way. In terms of picture results Aperture, when we went Mac, I downloaded the LR trial (we got Aperture bundled) and I carried out as close as I could, the same edit on the same file in both (not easy when of course all the sliders are different). I use Aperture to import the photos directly, I'm not sure where the setting is for whether Aperture is going to store the photos in it's library or on the harddisk (it might be in the import dialog, I can't get at the machine at the moment to check). I've also set Aperture to use a directory structure that both the Canon ZoombrowserEX and LR used for importing on the PC, it was what I was used to, this is adjustable in the Aperture import dialog.
Yes, Aperture produces a TIF for passing the file to an external editor and LR to PS doesn't (I believe, I can't remember now sorry), but when you save the results from PS you can't save the changes back to the RAW file anyway, so I don't see this as too much of an issue. If I want to use ACR on the RAW file directly, I'll open it straight in PS instead of using the Aperture Edit With dialog. As with LR, Aperture doesn't make any changes to the image files, and only saves the changes to a resulting image file on export. You can specify in the export dialog of Aperture where you want the resulting files to be written, same as LR.