A few suggestions - first, at this point in the evolution of technology, if you are buying a new rechargeable tool, it makes sense to go with lithium batteries.
Second, think about what other tools you might want to have in the future, and whether you can build the desired selection within the offerings of one brand. For years, I have had a B&D string trimmer. This past spring, Wife decided she needed a reciprocating saw for pruning the jungle around our house, and it's really convenient to have both tools use interchangeable batteries that I can charge at one charging station in the garage.
Third, like Elwin, I have had a number of Riyobi tools over the years - they aren't the best out there, but they are good, reasonably priced, and the line is designed around the concept of interchangeable batteries that all use the same charging station. And a subtle point - older Riyobi NiCad batteries and tools are fully interchangeable with newer Riyobi Li batteries and tools. The only constraint is that Li batteries can only be charged using the Riyobi Li charger, but the Li charger can also charge the older NiCads. Last year, I bought a couple of replacement NiCad batteries for my old Riyobi NiCad drill. Unfortunately, a few months later, the drill died. I bought a new Riyobi Li drill with two batteries and a charger, which can take either the new Li batteries or one of the replacement NiCad batteries.