electric strings are steel / nickle and will react stronger to a mag .
most acoustic strings are bronze wound etc ... a mag will still read them because they have a steel core , but it will sound "muddier ' .
then again , some folks like muddy .
I was told acoustic strings are bronze wound with a iron core while electric strings are steel wound with a iron core and are much more easily read by magnetic pick-ups.
I use anything laying around.But have only used piezos.I have abuild coming up w/ a lipstick/tube style pickup that I'll probably use electric on.