We did both of them on our last trip if you want to read my reviews:
May 2017 Dining Trip Report
I would say they're hard to compare though because they're so different. It would depend if you want something for a special occasion or just a really good breakfast before a park day. We loved both, but CG brunch isn't something I'd compare to the other breakfast buffets on property.
We did CG Brunch for a special occasion, it's definitely a lot of money for meal, but it's an interesting restaurant, you can come back for the fireworks later (though I think that vantage point made more sense for Wishes than HEA because of the projections), you can order multiple entrees (which made me feel a bit better about the price), and theres an appetizer buffet/dessert plate. We also don't like sushi and I still feel like there was enough other food that we got value out of it, if you like sushi though it might feel even more worth it. I would also do this when you don't anything planned for the early day (and I think it's only available on Sunday) because you'll want to take your time.
Boma is my favorite breakfast buffet on property but it isn't anything fancy or "extra", and it is a bit out of the way if you aren't staying at AKL. However they do have amazing bread pudding, make your own omelets, and tons of other great food, along with a much lower price tag.