your ambient case temp should stay low enough that it doesn't matter that you're blowing "warm" case air into the radiator and out of the heatsink, because really the case air shouldn't be much warmer than room temp.
as for which SIDE of the radiator to put the fan on...it doesn't really matter, attached to the case or attached to the radiator (which is in turn attached to the case) should really bring the same results.
if for some reason you think your case temps ARE going to be hotter than outside (even given your presumably 120mm fan(s) and whatever other 80/92mm fans you have on there), then you MAY want to blow into the case over the radiator, which will of course heat up the case even with decent airflow
my plan for mine: radiator stuck on case (on back, no room for blowhole on top with my mid tower), fan blowing through it, outward, two 80mm fans blowing in (side panel and front)
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