Acrobat

Once you have changed the default opening application from Acrobat to Apple's Preview on that Get Info panel for a PDF, it is important that you click the Change All button located there, and follow through with it.

There will be a secondary dialog after clicking Change All… and just click Continue on it. That ensures that all, not just the current PDF, will be opened by Preview.

Highlight a pdf and control click Get Info > Open With and select default for which application you want pdfs to open with.