Smaller pore sizes and smaller filters clog faster. Carbon filters trap pesticides and metals, which for my taste is a worthwhile feature. Ceramic-only filters do not. For emergency or short periods of developing world backcountry use, filters such as the PUR Voyageur, PUR Scout, and Sweetwater Guardian with iodine cartridge are good choices. Note again that a water purifier is not a requirement for developing-world travel.
Most travelers buy most of their water and use iodine tablets or drops in a pinch.
I have not been compensated by any company to plug their products. Pumps about one liter per minute. Screens to 0.2 microns. Pumps about one liter per minute. Carbon filter screens to 0.2 microns.