You'll be happy with either one of them and both will have people that swear by their brand. The Milwaukee's have batteries with a charge indicator on them so you know when they're about to die, which isn't always the case with Lithiums. I believe Panasonic makes the batteries for DeWalt and Makita as well as others because there are only 2 or 3 companies that make rechargeable batteries for power tools.
We just bought 4 M18 combo kits for our shop because a couple of our guys are loyal to them, as is the boss, though all brands, including Milwaukee are made overseas. When I worked in the tool department at Home Depot for 6 years and this question came up, I always said that in most cases, it's a Ford versus Chevy type of thing. If your dad drove one or someone you looked up to did, then you'll be more likely to prefer one brand over another. I told people that professional craftspeople were often dedicated to Milwaukee like Volvo drivers are to their Swedish tanks. They used to cost a little more than other brands, but that has changed a little in recent years.
You'll be happy with either one of them as both will have professionals that will only use their brand. The sets will have similar features and specs, so it comes down to who do you trust. I've used both of them and the people I work with have both, too. They are both durable tools and hold up to heavy use in industrial settings.
Cabinetmaker and carpenter for more than 20 years and a manufacturer trained tool technician. I've owned and worked on all brands and would probably choose Milwaukee, but if there's a big enough price difference, I'd get the cheaper one.