I would probably go for the apartment in Wipkingen (if your decision is mainly location here) because it is not really far centre of things, plus has transport options, and that price is not bad. I don't know about Schwamendingen. Affoltern I think is far.. I have a friend living there and it is a pain to take the bus out there and at night after going out would need to take a cab back ($$). Anyways good luck with your choice