My BIL is a big Dewalt guy. I prefer much of their 18V lineup. The 12V Milwaukee stuff is way better than the 12V stuff in my opinionm
Discussion
DeWalt has the widest variety of tools in their 20v lithium. Everything from automotive wood working to lawn tools. That's why I picked DeWalt. If the only thing I did was automotive, I'd go with Milwaukee. I just wanted one battery system for everything.
I don't tend to care about having more than one battery system per voltage level. If I needed 20V tools, I'd probably buy Dewalt.