I would stay away from Hitachi. I have the 18V Hitachi (I own the drill, driver, 1/2in impact) from Lowes and don't get me wrong, it's an excellent drill, driver, etc, but the batteries are very expensive. They come with 1.5 Ahr batteries, and a 3 Ahr battery is nearly $90. You can only get the 1.5 Ahr battery at lowes. Charger feels like cheap Toys-R-Us plastic. 3 Ahr battery barely gets me through a work day on the drill. the 1.5 hr battery only lasts 45 min with 80% duty use on the drill. The impact is maybe 30 min at the most.
I would go with Milwaukee if you can afford it. Every tool on their 18v line is quality. Their 4Ahr batteries are $65 online, and an extra charger is $35 online as well. Although the tool itself is expensive, we run them here where I work because everyone else runs them so if you have a battery go down, or need an extra driver, someone else has it on site. The driver is high torque, nearly 1600 in-lbs compared to the 1200 in-lbs of the Hitachi. The main complaint is that the size of the drill is so compact, when you put your hand on the back of the drill to push into what ever you're drilling, then it gets very hot. The grinder is absolutely excellent for Milwaukee. Best cordless grinder my crew has seen on the job site.
If you want to spend less, and still get a quality tool, buy Ryobi. They have an excellent package deals with the soft case, battery, charer, drill, and driver. Their grinder is garbage, but their sawzall is good. Stroke is a little short but for a DIY'er it doesn't really matter. I've seen a lot of Ryobi deals recently.
I would stay away from Dewalt. We have had nothing but problems with every Dewalt 18v tool we have had here on the job site. The battery is especially garbage. I've had several PCB's go out on the batteries, bad cells, I've taken apart and fixed more Dewalt battery packs than I care to mention.
Brushless is great if you can afford it. Higher battery life, more performance since it's more efficient, but it's close to double the current price of brushes. It has a direct drive instead of the induction coil since you loose quite a bit of efficiency with the gap between the brushes and coil.
I've seen a few deals on refurbished dewalt brushless, if you are determined to stick with brushless and dewalt.
PM me if you want more info. We just went through a Drill/Driver/grinder/sawzall 18V cordless phase here on the job site re-tooling up. I'm the project manager and I help the crew with the tech info on making purchases for their new 18v cordless packages.