Rasegan is stronger..
the generic rasengan is basically at its weakest form.. even with a tiny bit of nature manipulation its shown to become stronger than an average rasengan.. the rasengan can be made to increase in size and thus increase in power..
The chidori is at the strongest it can be as it is.. there is no making chidori much more stronger than it already is..
also lets not forget both have different pproperties and are both preferable in different situations
P.S there was no need to even bring this up, you only did it to cause a flame war.. Pointless~