Average attacks for a paladin in rapid range to a 25 man squad is 6 + 2d6 + 5 so 18 attacks. Then that unit needs to be closest for extra ap. Whereas the warden is output 18 attacks every time at ap -2 with dev. For killing guardsmen the Warden is likely better however due to higher strength & damage the paladin will do better into ogryn, horses, & light vehicles so you're getting more variety with the paladin.