in prinziple, both solvents are possible.. As far as I think, the main difference would be in the boiling points and therefore the different evaporation times leading to different fiber diameters. and maybe the differetn resulting viskosities. you may find the attached file interesting..

best

http://nopr.niscair.res.in/bitstream/123456789/2024/1/IJFTR%2033%283%29%20345-353.pdf

Primary difference would be the dielectric constant of the solvent, i.e ability to saturate charge leading to formation of fine taylor cone with continued drawing of fibres. Secondly, which is an extension of dielectric constant ,is  the volatility constant, more volatile, the drier will be the fiber. But remember it is the dielectric constant and applied voltage for a given fixed height control the diameter of the tail of the cone.

In practice, both solvents are ideally good for making PAN polymer dope for elctro-spinning operations; however, the difference lies in the their dissolution power related cohesive energy density. ; DMF has CED value equal to 141cal/ml. where as that of dimethyl acetamide is @ 123 cal/ml. This leads to slightly high dissolution power of DMF, which in turn helps in electrospinning stability ; avoiding lump formation/acculmulation of polymers/