Depends on the kind of Mac you buy. I can only comment on their mobile offerings:
- Best supported are the current MacBook Airs. Everything except the Webcam should work out-of-the-box. The webcam needs the out-of-tree bcwc_pcie driver (https://github.com/patjak/bcwc_pcie)).
- The Retina MacBooks need some manual work before being usable (e.g. need to compile out-of-tree keyboard & touchpad driver (https://github.com/cb22/macbook12-spi-driver)), but should work fine as well.
- The MacBook Pros before October 2016 are also quite good supported, the support for newer ones is still quite incomplete (check out https://github.com/Dunedan/mbp-2016-linux for details), although it's possible to use them as daily driver if you're aware of the limitations.
All of the Macs I have require binary firmware blobs for WiFi, for the open source driver to work. And even in that case none of them can do even 802.11n. I have to use the proprietary WiFi driver to get 802.11n or 802.11ac. And yes each model varies in this regard, which makes it something of a Choose Your Own Adventure book.