Hell is obviously the better choice, but nm is faster and its not such a disappointmant when she drops 2 eld and a tir. So far my best drop in hell was a single Tal rune, best drop in nm was 2 Io and a Ral. Maybe your best bet is a mixture of both - nm for volume and hell for occasional quality. And don't forget to look in the barrels and chests.
I have been wondering about the mf. Most of the time when people ask about whether mf effects rune drops they are asking "Will my sorc with 500 mf get better runes?" Many people ask this question because they use maphack which apparently shows runes above a certain number as gold (unique) items (which also explains how sorcs can tele in and pick up that ber rune that just dropped in a baalrun and grab it from amongst all the junk on the floor). I think a better interpretation of the question would be "Will my 0% mf zon get more rune drops?" Runes are not magic, rare or unique. They are white items. Your mf% determines how often blue, yellow and gold items will drop and the higher your mf the less white drops you will have. I would be very interested to know if this works - last season my zon got about twice as many runes as my sorc (0% mf -v- 4xx% mf).