I've been using the heck out of my 18v DeWalt stuff for years now. I guess I've had them for about 7 years or so now. At about 5 years the batteries started to really fade. Rather than buy new ones, I took a chance and sent them to a guy who advertised on the internet that he "remans" them for about $20 a battery. I had them reman'd by him a couple of years ago and they are still running fine. They actually seem to run better than new. I got one "new" (couple of years ago now) battery when I bought the 18v DeWalt grinder, and my remans last just as long. As a side note, that 18v DeWalt grinder has been amazing! It will eat batteries faster than other cordless tools, but it has great power. I've actually worn the brushes out in mine and had to replace them; $5 or so.
So, not just because I have 6 or 8 of the cordless tools and have to stay with Dewalt, but because they work well and hold up well I'd recommend DeWalt. As a side note, I used my builder's DeWalt 36 volt cordless driver one day. Talk about a beast! The issue is that it is so big and bulky, not to mention expensive. It lasted longer on a charge and was noticably stronger than my 18v stuff, but I really haven't been left wanting for more power than my 18v stuff has. His theory is that he leaves the house with 3 of his 36 volt batteries charged up in the morning and can work all day without worrying about finding an outlet. On some of his job sites there is no power. I don't have that problem, so 18v is plenty strong for me. (believe it or not)