They serve different purposes:
DMG (disk images) is just a container file format to solve age-old issues with multi-fork files and transfer protocols and intermediate hosts that can't handle them, by not relying on them in the first place. In addition, the disk images can use internal compression. Your users will thank you for not confusing them with file wrapped in file wrapped in file (although disk images themselves take some explaining initially).
PackageMaker is a full-fledged installer package builder. You can customize the installation process and locations, do sub-installations and pretty much anything else you could possibly need. If your installation entails more than just dragging and dropping an application bundle into place, this is the one to go with.
From your requirements, the choice seems obvious. Since an installer package is itself a bundle, I'd say: create an installer package with PackageMaker and put it in a compressed disk image. Distribute the disk image to your users. It just provides a nicer experience.