Drinking water treatment judged by what it is certified to remove: NSF/ANSI 42, 53, 58 and 401, filter media types, and flow rate trade-offs.
RO is the only domestic technology that removes dissolved inorganics — nitrate, arsenic, fluoride, TDS. It also produces wastewater, works slowly, and is more system than most municipal supplies need.
The form factor sets a ceiling on what a filter can achieve, because contact time with the medium is what removes contaminants — and a pitcher cartridge has very little of it.
Filters are certified for named contaminants, so the first step is finding out what is in your water. Your utility publishes it annually, free, and it makes most of the decision for you.
A filter certified to NSF/ANSI 42 is certified for taste and odor — not for lead, not for anything with a health effect. The standard number tells you which claims were actually tested.