The way I look at it, I would look at what tool families have that you want, that others specifically don't have. If you're looking for the biggest family, DeWalt 18v is it. In every category, those Dewalt 18v tools are among the top but are not the top tool in any anymore. DeWalt 20v is attractive, but while the family isn't as big, DeWalt's version of the story is they designed every part of every one of those tools which is not commonly done if you believe them.
Milwaukee M18 Fuel is great. If I had to do it again, they would be on my short list. Bosch 18v used to have great tools that were really sturdy but not a lot of variety. Now, they still may not have the most variety but they make up for it with physically the toughest of all the 18v tools. You'd be more likely to break a tool from another brand than any of my Bosch.
Bosch has also taken care of me quite well with warranties, real American people on the phone (and very short hold if there is one), plenty of sales and rebates for cheap/free batteries, which is important primarily if you take advantage of their frequent sales on bare tools. Among my 9 tools I have 11 batteries, 4 big 7 slim and at least 4 chargers. You want a complaint? not every tool has a hard case. Their bags are nice but I don't think they're any more sturdy than any other tool bag.
I will include Ryobi & Porter Cable in my comparisons below simply because they make sense in some situations. My recommendation to you would be choose between M18, Bosch, & DeWalt, choosing which of the two DeWalt families to consider. The other reason I prefer the M18 & Bosch is the 'flat' style of batteries compared to the DeWalt 18v's stem. They went with a flat style also for their 20v Max.
I would not consider Cman, Ridgid, and I should include PC & Ryobi in this part as well. You can buy all 3 of the major brands mentioned in at least 2 real stores in whatever town/city you're nearest. If Sears isn't convenient and HD is, Cman would be useless in the middle of a job, and so on. This is more of an argument for the DeWalt 18v tools than anything else though, any pawn shop, ebay, and all major retailers have plenty of DeWalt 18v tools.
They all have tools that can be put into categories of drills/drivers/impacts, saws, and misc. Whichever set you get into, do yourself a favor and get the biggest, most inclusive set you can afford for your initial purchase.
- There are plenty of reviews of drills & drivers, increasing reviews of impact drivers as well as impact wrenches for those who choose to make the disctinction, though I personally only care for the impact drivers and try to do the big heavy impact fasteners with air.
- For saws, everyone has a circ saw. You might care if it's lefty or righty, otherwise almost all the 'big' kits (3-4 or more tools) include one and I'm sure you'll find a use for it here or there but it's not going to make or break your decision. All 4 have reciprocating tools but look at what's available from each. PC has a saw on the horizon that could be very useful to some but many others may not have a need for it. Cordless bandsaw may be useless to you but all 3 big ones have it, PC & Ryobi don't. They all have cordless jigsaws.
To me, the 'misc' is where the decision is made. What else can you do with the batteries?
- Ryobi. DeWalt, Milwaukee & PC all have 18v vacuums for example. There are 3 different kinds with the PC & Ryobi being very similar, and 3 different price points.
- All 4 of those also have Radios, though DeWalts does not support their 20v. Among the 4 I think Bosch first, Milwaukee second are the two I would want.
- They all have angle grinders, but only Bosch has the die grinder. Only DeWalt has the drywall cutout (Dremel type) tool.
- Ryobi, DeWalt & Milwaukee all have caulk guns.
