I've been lurking on Garage Journal for a while; this is my first post but I'll weigh in since I recently pulled the trigger on new cordless tools. I looked hard at DeWalt, Milwaukee and Ryobi tools to replace my mega-cheap Northern Tool cordless drill with something high-quality; I ended up selecting DeWalt 18V based on my own prior experiences with them, the wide variety of tools available and the total interchangeability of their 18V tools and batteries.
Ryobi makes good tools at a very good price point; if you are primarily looking for DIY woodworking tools, they are a heck of a bargain, and I know of a few contractors that are very happy with them as well. As mentioned above, their 1/2" impact is rated considerably lower than either DeWalt or Milwaukee; for me, this was Ryobi's downfall since I want a decent 1/2" drive impact.
Milwaukee's stuff is nice, and their 1/2" impact has a higher torque rating than DeWalt's; however, their stuff also tends to be a little more expensive. They also changed batteries a few years back, and I don't believe the new batteries interchange with the old tools or vice versa (someone please correct me if I'm wrong here). Milwaukee only offers lithium ion batteries these days, which have their advantages over ni-cad but are also more expensive. That said, I don't think you can possibly go wrong with Milwaukee if you want to spend the money.
DeWalt was high on my list from the beginning; I spent a couple of summers working for a company that builds grain bins, and I was sold on DeWalt's durability after seeing the abuse our drills and impacts would stand up to. It also seems to me that DeWalt has the best selection of 18V tools, but I haven't compared lineups to verify this. I do know that all of DeWalt's past and current 18V tools and batteries are interchangeable, so any used tools I would happen to pick up will work with my existing batteries; my dad also uses DeWalt 18V tools, so our tools and batteries will interchange as well.
DeWalt still offers ni-cad batteries; I can buy two DeWalt high-capacity ni-cad batteries for the price of one Milwaukee lithium ion battery. If I want to make the jump to lithium batteries later, DeWalt's li-ion batteries will fit my existing tools and the li-ion charger will charge my existing batteries. It is true that DeWalt's 1/2" impact has a lower torque rating than Milwaukee's; however, I have never been unhappy with the DeWalt cordless impacts I've used, and I can take the money I save over MilWaukee and spend it on air tools or extra batteries.
I have never heard anything bad about Makita tools; I believe their 18V 1/2" impact is rated between DeWalt's and Milwaukee's. Snap-on makes unbeatable cordless impacts, but they are expensive and don't have the selection of woodworking tools if you only want one set of cordless tools and batteries.
Your mileage may vary from my observations above, but that's my perspective as someone who has just been through this process. Seeing it in print also helps me convince myself that I made the right decision!
Isaac
