As a homeowner/DIYer I went with the Ryobi One+ line. They have kept the battery interface the same from nicad to first gen li-ion to newer li-ion. They have probably the broadest line of tools using the same battery, and are good enough for heavy DIY use. I did burn out a compact drill-driver driving 3" screws in bridge timbers. My friend was using it, and I think he had it in high gear, because it twisted his wrist in low.
You'll get ridiculed on job sites and not taken seriously if you're a contractor, however.
Compact drill, hammer drill, impact driver, 6-1/2" circ saw, recip saw, 4-1/2" grinder, die grinder, 34° framing nailer, lopping shear, hedge shears, led light, caulking gun