lens quality/choice makes an obvious difference, that aside individual pixel size of the 4MP sensor compared to the 2MP sensor is a defining factor for our purpose, sensors that are being used at their native res offer better results than ones that are binning, interpolating etc
in marketing speak there's always an assumption that a bigger number is somehow better, 4MP must be better than 2MP, 170° viewing angle is better than 120° viewing angle etc, the cheaper the product, the bigger the claims like it somehow means it's better, sadly a lot of consumers fall into the bigger must be better trap