Basically, ATCC recommends calf serum (CS) instead of fetal bovine serum for NIH 3T3, what are you experiences regarding these serums with these cell lines.
I have previously used both NIH and Swiss 3T3, and have found NIH 3T3 to be a bit more difficult to work with. In both cases, when culturing cells which have been previously confluent, I have seen no real difference in viability/phenotype or morphology between those cultures using FBS or BCS. 3T3's tend to grow pretty quick once you have them established!
However, when I first thaw cells, the viability is much higher using BCS. There are a few papers which suggest that this is because the BCS contains additional growth factors, but I can't find a solid reason. If you're going to use BCS though, I recommend ensuring you're going to use the same batch, as variability in cell phenotype between BCS batches is reported.