So what can I expect for breakfast at the various brands (as a Gold or higher)? I prefer something like HGI or Embassy Suites, where there are plenty of hot protein choices, rather than the low-quality, carb-focused buffets that most chains offer. As a Gold or higher, would breakfast be free at all of them?

Breakfast is the one benefit that has kept me with Hilton, especially HGI where you have a combination of a decent buffet and cooked to order items.