I'm a big Milwaukee guy, from power tools to hand tools, and I use them A LOT.
The M12 platform is solid all the way around, and the M18 platform is professional grade as long as you stick with the FUEL series of tools. I beat the snot out of mine and they keep on going, and that includes the batteries. I've had some batteries for almost 10 years, and they still work well enough that I am not ready to throw them out.
Their hand tools are VERY good, with excellent durability. I have their wrenches, flex heads, drivers, sockets, impact sockets, extensions, swivels, etc., multiple variations of their screw drivers, additional ratchets in multiple sizes, and they have all been good with the exception of the 1/4 drive socket wrench. For some reason, it would bind on me if I tried to put too much oomph into turning a bolt that wouldn't budge. I contacted Milwaukee and they immediately shipped me out a brand new one, free of charge, no questions asked. That's great customer service, and I'll stick with a company that has a great product with great customer service.
If your looking to do mechanical work, I would HIGHLY suggest the 3/8 stubby impact, and a 1/2 mid torque impact. Those two impacts will break free just about any bolt on a vehicle. Next on my list of must haves for the mechanic is a 3/8 ratchet wrench. With those 3 items, you can tear down just about any vehicle from bumper to bumper.