It varies depending on many things. First off what season it is. In a few seasons it's clear that some rangers are stronger then a pervious one, in Zeo it was stated that the Zeo powers were infact stronger than the Mighty Morphin powers. Second the indiviudal ranger. the Additional Ranger (Usually the 6th) is shown to be stronger than the others, even the Red ranger. Third, is it they're first time Morphing. Often done for hype, the first time a new ranger is introduced, they seem way beyond the normal levels of Ranger Power, possibly because of the human body gaining this massive surge of energy for the first time. All in all, it's very hard to determine. Some Rangers in they're cavilian forms have been able to hold they're own against monsters.