Ryobi
Fight me!
For the casual user or even hard core DIY-er I think cordless Ryobi tools are dang near perfect.
Price - they are cheap, tools are cheap, batteries are cheap, accessories are cheap. I feel the batteries have also come down in the price since I started buying them.
Customization - I think they have many different versions of the same tool depending on needs. Drills and drivers they might have 6 versions of each. This is also very true with their batteries. IN a drill you might not need a huge battery, and lighter is better. But in a saw or yard equipment you will want the bigger battery. You can also find great combo packs online with a little snooping. Sometimes you can basically snag a free tool or battery when you buy one they throw in the other for free.
Flexible - all the tools work with the same battery. All chargers work with the same battery. I can keep 2 on the job-site, 2 at home and 1 in the car at all times and never miss a beat. They make everything from tire inflators, to bluetooth speakers to lights. Can' beat the selection.
I get that dewalt is likely a "better" tool but the price is a huge hindrance to me. I would hardly want to use a $400 dewalt drill. Id worry id break it our get it stolen, if someone rips off my $50 ryobi impact driver NBD. I feel the higher brands are kind of the F150 Larient edition of tools. Sure you can tow 50,000 pounds through a mountain pass in the snow, but why would you?