Fotomagico is probably the best in terms of features, flexibility and just a very well polished 'mac' experience. The 'home' version is a very good value. I opted for the 'pro' version because of the Aperture support and HD export, but it was kind of pricey. I've used it to make some great slide shows though.
I didn't upgrade from version 2.x to the recently released 3.x. I thought the upgrade price was too high for the new features involved (for my needs). Had they cut the upgrade price I would have done it.