There's nothing wrong with mixing brands unless you're trying to keep an extremely consistent aesthetic. In my experience over the years, no one brand does everything or even most things the best. It varies based on both component and even the generation of product being released. And even the best of a brand may not be as good as products from other brands. Research what you want, and compare price to performance to find what's right for you, along with avoiding anything with lots of bad reviews or bad company support. Sometimes it does simply come down to brand and aesthetic preferences.